One thing we've not really covered in this thread (at least my cursory inspection of some posts give me that impression) is that IOs (and doubly so for invention sets) create a whole new reason to play a character. That in itself was great for the game, players and characters.
Whereas previous to IOs, often people would roll a character, play to 50, fill it with SOs, complain about ED, respec it properly, shelve it and move on to the next. With IOs and inventions it gave characters a new lease of life and a life beyond simply reaching level 50.
That in turn added a lot of new dimensions to the game which by definition rebalances (but not unbalances) it