I thought TBC class balance was pretty decent. I knew Gladiators who played Warrior, Warlock, Mage, Paladin, Druid and Shaman. And during raids a lot of classes were viable, 5man heroic pugs had a class balance issue due to CC requirements but raids not so much. In endgame raids I saw almost every spec, I played a Fury Warrior, a top tier dps class but a lesser desireable due Arms warriors bringing more raid buffs (but less personal dps), but it balanced itself off for many guilds. Really, you said yourself that you didn't play TBC much and it shows, in endgame raiding and PVP the class balance was really good... In relative terms.
Vanilla was broken by todays standards and for sure the game being new is the single most important factor, but people still play Vanilla private servers. Just as they play TBC and Wrath servers... What will interest you though is that the Cataclysm private servers are more popular than any of the others, followed by WOTLK, and the TBC servers trailing way behind in popularity, maybe even less popular than Vanilla.
The private server popularity tells a different story to what the forum posts show. Cataclysm servers are where people want to play, and despite the fact that they are buggy messes compared to the other expansion servers, they are still more popular.