I think you just crossed the threshold with this post. I think it's at 5 posts.
Hopefully you get replies from a better player than me. I love playing wizards, but am not great at it. Here are my thoughts about Aloth and wizards generally.
On normal difficulty using them as nukers is very viable. On PotD the enemies have much more health, there are more enemies, and they have better defenses, while you don't do any more damage than you did on normal. Using wizards as nukers in this context is tough until you have a deep array of spell levels to draw from, and even then it's usually not the most effective thing. What you want is to debuff enemies or create situations that multiply the damage your team is doing. If those spells also do damage, even better.
A wizard's first priority is to protect herself. Wizards can actually become quite tanky with the right self-buffs, and with good stats the cast time on those can drop to .3 seconds, meaning you can get all your meaningful buffs off in less time than it casts to get a single nuke done. You also want, imo, to get Deleterious Alacrity of Motion in as an early cast; spellcasting velocity matters, and a wizard typically has a lot of spells that she wants completed all at once in any given situation. The faster that happens, the sooner the fight swings decisively in your favor.
The next priority is to apply the nastiest debuffs you can to your enemies. This is hard on PotD (enemies with high defenses) and really rewards being aware of the different defense types and which spells target which defense. Mouse over each enemy to see where the weakest common defense stat is, then choose your aoe spell that hits that defense and drop it. Afflictions are mostly pretty damaging, especially level 2 and higher afflictions, so you ideally have an arsenal of different aoe spells that apply meaningful afflictions and target different defense types. I'd call that any wizard's #1 priority on PotD. Again, doing damage is a bonus.
Combusting Wounds is great because it's a damage multiplier. It doesn't do damage directly. It puts an effect on each target it hits that gives them a stacking damage over time effect each time they take damage from any other source, including whatever damage spells you cast and whatever your teammates do. My only gripe with it is that it's hard to see the damage it does. Chill Fog is an aoe spell that drops a patch that pulses a damage + blind affliction at regular intervals. You can see how this goes well with Combusting Wounds, because each Chill Fog pulse adds another fire DoT to anybody affected by both spells. It's an early powerhouse combo and never really becomes obsolete, just less obviously the best thing to do as you get more options.
Another thing to pay attention to is whether spells are Foe-only or not. Some spells can be finicky to target - non-foe-only cones, for instance, can be tough to maximize the value with in close quarters since you often have to run to the ideal spot for best coverage.
Also, once you have debuffed enemies, their defenses will have dropped and your spells that target that defense will become more damaging on average (because your hit numbers will rise correspondingly, resulting in more hits and crits). So pay attention to which damage spells target which defense so you can optimize your post-debuff damage contribution.
Once the enemies are thoroughly debuffed and their game has been completely ruined, then go ahead and start dumping pure damage spells; whichever you have remaining. Your job is basically done and you are essentially helping your team with the clean up. At early levels you can run out of spells and fall back on dumping autoattacks on enemies or using scrolls that don't seem like they'll be critical later (low level damage-only spells, mostly). You can also use the renewing necklace of fireballs trick (putting a nearly depleted necklace in your stash with a full necklace makes them both full) once you have two of them to dump fireballs on people if that doesn't feel exploity to you.
At least, this is how wizards have worked for me on PotD. On Normal (and in the original PotD, honestly) they were basically gods dispensing various forms of punishment or death at will, but on the current game they need to focus on turning the enemy's offense into pudding.
Unfortunately, choosing the optimal spells on levelup really requires a bit of metagame knowledge about which grimoires are out there, containing which spells. With that kind of foreknowledge, you can get the optimal grimoire as soon as possible, and you can focus your spell picks on spells you always want in every fight and leave the situational spells (damaging spells that target specific defenses) to the right grimoire that you then ideally swap out for the correct fight. It's not breathtakingly suboptimal to play without this, but if you're like me you get to a point where you want every spell level to have one aoe debuff, one buff, and one useful damage spell, so if you whiff with a vital spell and have to deplete that level with a second cast of it, you're not completely without backup options from other spell levels. Not necessary for your first playthrough, though.