I suppose, to me, the answer comes down to a balance of what's the best for class changing at 11, and what's the best overall once you've fully powered your party. To me, it comes down to - what are the most powerful equips in the game, how many can you get, and which classes can use them. A thief over a 2nd fighter essentially comes down to ensuring nobody in my party ends up using 2nd best equips. SE really balanced the loot offerings in their special dungeons for a balanced party of no duplicates. Since the classic party is capable of class changing at 11, and I'm capable of class changing with it at 11, making any further concessions for the sake of such, if such changes negatively impact my tweaked out final setup, seems self defeating. I suppose what it comes down to is, there's no way to change any lower than 11, so that sets a threshold that really need not be exceeded in terms of choosing classes for early power vs late.