Problem with this game, and prob others that rely too much on tabletop rules is that in order to gauge the true power of a class is for it to be mid to late game. So many of these classes take the first like 10-13 levels only to then come online, especially the magic types. So you use them as CC whores in the beginning of the game because their dmg is so shit and not only that not enough spell slots or you have to rest every other fight. So best way to try some shit is first get to lv 20 and complete base game, then it opens you up to creating other lv 20 full fledged builds and try different shit.
You can also get the mod that you can give yourself cash so you can afford to buy other slots (and fully respec the companions). IDK why they make it so expensive? I guess they want you only to play with the given story companions, which is OK but leaves SO many choices behind you cant try. And I mean you can play through the game once, twice, maybe three times but after that you just want to create some classes and go hit up the endless dungeon for some funsies. IMO like 3/4 of the fun in these games ends up being building out some classes and trying different shit. In kingmaker they had this other mod that added way more options to build out your characters too, especially for casters. I guess they come from Pathfinder some other module or some shit? Anyway, yeah you could build some tough ass casters.