I agree with the notion but I've always felt that certain late additions beg the question of why they had not been encountered before. Kind of how Zack appears in BBS but is never seen again. Then again, there is supposed to be many worlds out there so it's plausible to think there was never any reason to visit non-Disney and non-original worlds. However, they might have the same problems as that of Disney worlds where they are loosely related to the plot and we come back at the same point we are now.
It's assumed that Sephiroth killed Zack, which would make sense as to why Cloud was there in KH 1.