I think the thing people aren't taking into consideration regarding "min-maxing" your party is that Larian is balancing this game for a 4 person party, so this should become way less of a concern. They will likely have to consider things like alternative tactics and strategies for specific fights due to the 4 party limit and the possibility you won't have X class with X spell/ability. Like D:OS2 I'm sure you'll be able to mod in a larger party, but just like D:OS2 it'll likely make the game completely trivial in every encounter due to the nature of the game balance.