It's not just scaling humanoid parties in BG though. If you're high enough level, monsters are added or replaced, sometimes very powerful ones.
Which, if there was ever a form of "difficulty scaling" that is acceptable from an immersion standpoint, has to be pretty much the best possible solution.
I'm fine with encounters getting more challenging. I'm not fine with having the SAME CREATURES scaled up and down. Consistency is an important part of what makes a setting somewhat believable.
