I'm gonna throw my own view on the pile here and say that even though I wasn't a fan of the per rest system, this system in my eyes has a LOT of problems right now. Get ready for a lot of in-depth reading though, cause brevity is not my forte.
In the per rest system, I felt classes like the Druid, Priest and Wizard were more or less a ball and chain around my ankles in many fights early in the game, likely to compensate for the power their abilities provide relative to someone like a Paladin or Fighter, whose per encounter abilities feel like a joke in comparison. Until I got to spell masteries or a sufficient number of spell tiers that I could "waste" in an easier encounter just to make things go faster, these caster classes were limited in what abilities they could use in consecutive fights, often resulting in just autoattacking because the out-of-combat resources of camping supplies and gold were limited in the very very early game (like early Gilded Vale). After that, it was a question of how much you want to run back and forth for camping supplies (and considering PoE1's load times, that usually meant just not using abilities unless necessary). Gold became way too plentiful and camping supplies and rooms in the inn were dirt cheap, so the only issue was that of time you spent going for a nap. The system devolved into a time-saving exercise rather than one of strategic significance, since you were never put in a situation where you simply could not get out of an area to go pick up more camping supplies or reaquire that resting bonus from an inn or stronghold. The resting system simply becomes meaningless if access to the resource your resting consumes is plentiful, cheap and at all times unrestricted (except for Sun in Shadow, but there are piles of camping supplies right in the starting area and by then the fights are not a challenge even on PotD). HOWEVER, even this twisted incentive to rest as little as possible to save time (not resources) was usually good enough to get me to try and optimise in every fight so that I don't lose unnecessary health and force an early rest and bunch of backtracking.
PoE2 has a different problem, one of a shared resource pool (and no, I'm not talking about the combat resource system). The significance of each fight is limited to "does my party get wiped?" If the answer is no, the fight does not matter. And the problem comes down to the same thing as in PoE1 though with different consequences. Once again, the resource your resting consumes is way too plentiful. The food you use up for resting and removing ALL your injuries is the very same you use to feed your crew. That could be a good thing, if supplies were limited and you had to weigh whether or not you can afford to rest, whether you will have enough cash to restock, whether you will be able to feed your crew if you **** up in the dungeon, etc. But it's not limited. You get PILES of that stuff. So not only are you not restricted in feeding your crew with your 500 veggie and 300 fruit piles, but you can rest as much as you want, with no backtracking, no in-combat or out-of-combat resource restriction, just...rest as much as you want. 8 times, back to back. Knock yourself out, because it doesn't matter.
With that comes the spellcaster routine. There would be no point in having per rest abilities on spellcasters when you can rest as much as your heart desires at any time, anywhere. The time-saving aspect from PoE1 isn't there because you don't need camping supplies, you need food, and you ALWAYS have food, so you would just rest back to back after every fight if you had to. That results in spellcasters having a routine each fight. You can use all your abilities, so you just set up a cycle (queue Eldritch Aim, Tayn's Orb, Chain Lightning twice, Pull of Eora, Delayed Fireball, Fireball, now press space and watch the fight resolve itself). Every fight becomes the same cycle for all your characters. It would take an extraordinary fight type (fighting a large merc company vs fighting a single dragon)/difficulty spike to occur for the routine to change.
Which brings me to difficulty. Granted, I haven't quite finished the first campaign yet. I'm currently resolving the last town I haven't done (Crookspur) and I'm set up for the final stage of the final quest. But so far, I have had ONE, count them ONE area where I had problems (because I went in WAAAY too early) and the rest was a snoozefest. Due to the open nature of the world map in PoE2, you're going to end up doing things completely out of order. All the time. In fact, having spent quite a good deal of time thinking about every quest and area and its difficulty, I still have no clue what the correct order of doing things is (where in PoE1 that was pretty self evident with the exception of Endless Paths and White March expansion content/some bounties). To that end, I believe the game HAS to be played with level scaling on (upwards only) by default if you don't want 90 % of fights to be you just pressing space to unpause at the start and letting it play out. You can level up through so many quests without fighting that when you do get to fighting, most of the things are way too weak to threaten you without scaling. You're not even incentivised to optimise in the "trash" fights because with the lack of long-term health and resources, all you "care" about is a character not getting knocked out (but you don't really care cause you can just rest instantly). You can easily autoattack through an entire fight because there is no long-term plan in motion, no attempt to conserve resources (time, camping supplies, spells) so you can just let things play out or just spam all your most powerful spells, up to you. Then again, level scaling will result in a problem I already mentioned before, that is, the routine. If all fights that are not way above your level end up having a more or less flat difficulty due to level scaling, there is no reason for you to deviate from the ability routine you already have set up. And since quests have an indicator for which ones you are ready for and which ones you are not, it's going to be rare for you to take a surprise buttkicking (like you would, say, showing up in Cragholdt at level 13 in PoE1 or trying the Alpine dragon at lvl 11).
To not be overly critical, here are the good points of the system and where I see potential in this greatly improving. Spellcasters are no longer a hindrance early, which is great, and you get to utilise all your characters fully at all times. If the combat scenarios were a lot more varied with significant, non-ignorable differences in enemy weaknesses and attack strategies, the spellcaster routine wouldn't be a thing and you'd have to use all the tools at your disposal at all times to make it out alive. You'd have to protect your party from charm attacks from fampyrs (btw, where are those? haven't met one yet, they were all over the place in PoE1), or have to deal with immunities (so suddenly your damage spell of choice can't be used), have enemies ambush you from behind (so now you're in mad panick protecting your spellcasters from interrupts, which, btw, are a great improvement over the PoE1 system). But the scenarios are mostly all the same, and since the only battles that matter are the ones where your party gets wiped, that MUST NOT be the case, otherwise, no fights matter. As it stands, combat is always the same. You walk up to the enemy, and either sneak and attack head on or talk and attack head on, or board their ship and attack head on. Very few ambushes, very few fights where adds spawn in unexpected places (Alpine dragon, I'm looking at you) or where you're brutally, brutally outnumbered by powerful enemies (Magran's Faithful, I hate you and love you at the same time). Very few areas where things are consistently just powerful and kicking your butt unless you intentionally go in too early. The one single area that gave me problems and that I would praise is the Old City Ruins dungeon in Nekataka. Since the lift gets pulled from you if you spend too long down there, you are suddenly trapped in a hostile environment and have to fight your way out (and hope you're strong enough to do so) to get back to civilisation. Having gone in way too early, I had trouble making it through like 5 fights without wiping. Even tried to race back through a few sudden spawns in areas I've cleared before to try and make it back to the lift before it goes up (and failed by about 2 minutes). That was great. The rest system still carried me through, where Camping Supplies would have not, which is a real shame. I could just chain rest after each fight if I felt like it with no consequences, where Camping Supply limitations would have made it so that I have to think and plan my route out of the hellhole I put myself in. Sadly, the Camping Supply system never took the opportunity to trap you somewhere and make you dig yourself out, and this system does not give such an event the gravitas it deserves. Lastly, I'd praise the injury system for its interaction with traps. Walking your Mechanics character into a minefield and realising midway through that you don't have the perception to detect half the traps and you already got 2 injuries...that's fun. What's not fun is that I can literally rest right there with my Rogue in the middle of a trap field and the rest of my party two rooms away in safety.
In my eyes, the fix to these problems would have to be two-fold, if we disregard the option of tying the rest system to a different resource (one that can become scarce without impacting the ship system's resources) and I believe it is very much doable with a few balance changes: 1) Make the difficulty more spiky or just consistently much higher. If the only fights that matter are those where you're at the risk of dying, then ultra hard fights in places where you do not expect them might be the way to go. That way you essentially have to try in every fight until you get a feel for its difficulty (meaning no autoattack autopilot) and you will frequently end up in situaitons where you have to redo a fight a few times to figure out its tricks (meaning that the fights have to have a trick to them though). This one has to be taken with a grain of salt, because it is possible that level scaling partially fixes this, and turning off the level indicators might also improve this greatly (so that you don't know which fights/quests to avoid). Hardcore mode (or Trial of Iron or whatever it is called) would suffer, however, since frequent difficulty spikes end up in dead parties. For that, level indicators would be required, which messes up Expert mode. Scaling things a little above your level (like when you High Level scaled White March when you were just barely above the level threshold and suddenly everything in White March was hard as balls) might be better in that regard. Simply put, fights have to be difficulty for this easy-rest system to work at all.
2) Make resting clear away only 1 injury instead of all of them unless you use extremely high quality food (that's rare as far as I can tell), and put a limit on the frequency of resting (one that cannot be bypassed by just Waiting, btw). That way, accumulating injuries in fights isn't meaningless due to the resting system. Currently, the only way you lose a character is if you either needlessly go into a fight/trap room heavily injured, if you keep resurrecting a character in a fight until they die, or if your whole party gets wiped. Accumulating injuries faster due to tougher fights and clearing them out only one at a time when resting, and not being able to rest more often than, say every two days, would mean that every screwup in a fight has longish-term consequences and triggering traps will make you rethink your mine-clearing line charge tactics. In addition, sealing a party away every now and then like you do for instance in the Old City Ruins would give the restriction a bit more meaning, since you can't just decide to spend the next 2 days running quests or sailing in circles around the island until you can rest again.
My 2 ce....my 2000 word essay.