Neither in NWN nor Fallout, I didn't see why AI-controlled party members are bad. I simply don't.
You should read the NWN:SoU expansion pack reviews and visit the message boards. One of the main complaints is the annoying AI, especially for spellcaster NPCs. As for Fallout, I got shot in the back by party members (with burst-mode weapons - ouch!) often enough to think that computer-controlled party members are not the way to go.
Infinity Engine games had AI-Behaviour. You could set an AI routine for your members or you could disable them. That's what I had in mind. I doubt those were THAT difficult to design.
True, true. But it was almost impossible to finish the games by relying on the AI scripts. I think most people just disabled them and controlled everyone manually, so IMO they were not worth the developers' effort to implement. Of course I might be wrong - it might be cheap and easy to do - in which case Larian will probably add an AI toggle. As long as you can disable it, I'll be happy.