Some people have reported that the difficulty settings don't change the spell resistance on enemies. I'd need to test it, but if true it'd put the "just lower the difficulty" into question if it is your spellcasters who are struggling to land a spell.
A pity you do not have spells that ignore enemy spell resistance in the videogame or feats and race or class features to improve your chances to ... hey wait!
PD: I checked and you were right, the Spell resistance is static despite your game options. The other stats of the enemies, number and frequency, the abilities they use, etc you can change.
Well sure. And I give credit to Paizo and Owlcat for setting up the rules so you still have fun feats after you've paid your feat tax. I never hit spell resistance because I've built that way. But it just underlines that a 3.5 mage needs to get to level 12 before it becomes functional.
But the DCs on some spells needs to change. Casting 16 -- not an exaggeration -- versions of remove curse to transform your party member from a dog to a human just isn't fun. Will I get the 20 this time? No! Do I sleep and keep up roleplay or do just break immersion and save scum . . .
So far for me in terms of quality its:
BG2ee > BG3 = Solasta (each has its strengths) > Pathfinder > DOS2