In short, spellcasters are only really needed for "trick fights". For shenanigans. For meme tactics. Not for general encounters. Also not even necessarily boss fights, unless a boss fight is also a trick fight.
I'm aware that this also has a lot to do with Owlcat's way of designing encounters, and not just because of the rule books. But how I feel about the way 3.5e treats casters is still the same. Making martial stronger is understandable, but the harsh punishment against spellcasters is too much.
It's not just trick fights. It is simply a different playstyle. With grease for example I didn't need a tank, because even on higher difficulties you could faceplant everything, starting act one. Same for stinking could (heightened it also worked against the final boss), a lot of battles I didn't need a tank because enemies were nauseated and didn't do anything. Later on there was sirocco and creeping doom. I'd also say that in my experience, when playing PK for the first time (no kineticists back then), it was just easier to buff your animal companion to use as a frontliner. If the animal companion died, a simple rest would bring it back. Of course now that kineticists are in PK, you could as well ask why bother with either fighters or spellcasters, when you can just spam deadly earth.
Playing WotR now, I'd say that it is the classes that can target touch ac that are most useful (deadly earth is slightly less overpowered due to trip immune enemies, but still...). Unique enemies often have very high ac but very low touch ac, while at the same time hitting like a truck. Because of how dumb the ai, I just find it easier to spam skeletons while using anything ranged with touch attack (conjuration tends to ignore SR, though Ember can manage with rays; for now I've decided to ignore the kineticist class). This makes a lot of these supposedly tough battles easy, like that summoned demon end of chapter two (I think his touch ac was something like 6?). Funny enough the lady who tries to summon him is tougher.
