Honestly, I think resting mechanics are pretty bad in video games in general because video games operate on a completely different level than a tabletop experience. You see, there is no DM in a video game, so nothing really stops you from abusing the rest system anyway, rendering it moot and something to be used in an options menu (maybe as a difficulty option?). Basically, why have a Per Rest and Per Encounter ability when I can either hike back to an inn whenever I please or just sit my booty down and camp to fix the problem right away?
I know it might get some people up in arms but it's actually really important in terms of game design. Are you just wasting people's time for "realism" in a game where people can just drink a potion or cast a basic spell to deal with literally any other health issue? Did nobody think about inventing the magical equivalent of caffeine since they solved their world's other health problems via potions and magic? As with anything, you could just build something entirely around a resting mechanic but it'll be a damn hard time balancing it so you hit the exact right pixel between "Am I wasting people's time by forcing them to rest constantly?" and "Why even bother resting in a dangerous place since I have enough charges anyway?".
Some games have attempted to solve this problem with random encounters on rest but that's pretty terrible for obvious reasons and hasn't been used in ages as far as I'm aware. You rest because you're out of spells/skills/whatever and/or have low health, followed by random monsters ruining your day and wasting your time. This is where a DM comes in to be lenient but a computer has no such distinction, it can only operate within the parameters it's given. So either you get swarmed by enemies or you don't - and god help you if the players figure out some health/spell value to achieve leniency vs harshness.
I'm all for it as an optional difficulty or roleplaying option. By all means, rest away if you find it fun and/or realistic but I don't think there's any really good option so far that has straddled the line between realism and wasting your time. I never really rested in the previous game outside town visits because it was lenient with charges and such - only severe screw-ups once or twice in a playthrough which doesn't justify an entire game mechanic. Honestly, I don't really think the mechanic was needed at all unless you did a blind first playthrough on PotD, at which point you're such a small part of the playerbase that it might be worth just relegating it to either be mandatory on PotD with limited resting at inns (maybe by making that absurdly expensive or something) or as an extra option as mentioned before.
Basically, this is such a fundamental game mechanic that it's at the point of either going all out and virtually eliminating resting at inns (either thorugh economy or just running around tiny villages where no one will take you in) or you don't bother at all and balance your encounters around having X abilities at Y levels among your party. I can deal with either but I'm not a big fan of this middlepoint we have currently and where video games tend to settle. Either I get to go all out all the time against tougher opponents or I get to optimize my resources and alter my gameplay via party class management and item management. PoE2 seems to tilt quite a bit towards the former option, which I'm okay with, but I can see why D&D traditionalists may not be fans. It's also arguable whether or not the opposition is tough enough but I'm not on PotD yet, as I'm doing my first playthrough on the 2nd highest difficulty.
This is no small or simple change to make in either direction, as you need to tweak basically every number in the game from the amount of money you get to how much health you have, plus it impacts your gameplay experience in terms of seeing major cities and such (the devs will have to find a really good answer for you either never visiting cities or never being able to find a bed in one). Interesting topic, though!
TL;DR: I write way too much. I'm sorry fam.