I've played it all the way until Sunwell. It's fine that it wasn't balanced, but it wasn't really broken in any aspect and almost all specs had their unique flavour. It's sad that you didn't enjoy your spec and it seems to affect your judgment of the xpac, but I don't see how that makes it so terrible.
As to what player group wants TBC, I'm not sure what to tell you. The best bet would be PvPers, since the balance was probably the best there (and I mean asymmetrical balance, not "butcher all classes and give them all the same utility within the same role" kind of balance). Other than PvPers, what player group wanted Classic? SOME of the old players and players who haven't played it. Certainly not all of either group. Same goes for TBC, I've read plenty of threads since Classic was announced and it really seemed like more people called for TBC servers rather than Classic. A game doesn't have to be perfect for people to want to come back to it.