Wrath was awesome. Before Wrath, Warriors were far and away the best tank "for reasons". There was no balance at all. Remember any Tankadins? Pallies might as well have been given a second healing tree like Priests for all the good it was. For that matter if your class could heal, you DID heal. The other trees were trash. And Warriors speced for Fury outfitted in raid gear were like Rogues in plate, completely obliterating the hybrid dps Shadows and Rets and the like were doing.
The raid utility was so overboard that by TBC you had Paladins standing outside sunwell buffing everyone between wipes because the raid still needed their buffs, but needed room for boat loads of Shammies for their blood lust. What people played was dictated by the raid utility quota more than their preference in play style, and that utility quota was sky high. Wrath actually let to run with your friends, as opposed to "That guy who's a douche that unfortunately has the buff my raid needs".
You are only thinking of balance issues, which mostly didn't matter except for raiding, as everything else was made so easy, almost anything could tank.
I am talking about the whole purpose of an MMO. MMO's are social games at their core, and WotLK was when they started killing the social aspect of the game for new characters and especially new people to the game. Balance issues will always exist as long as classes are different.
WotLK started the downward spiral of killing off important social constructs in MMO's.
Examples:
1) Forming groups used to require a social interaction by talking to people. They also made your ability to play an important aspect as well, as people will remember if you suck or not. Taking away the need to form groups takes away a lot of social interaction needed to make friends in these games.
2) Cross server queues for groups made it where even if you managed to find someone you enjoyed grouping with, you couldn't talk to them again, because they were on another server.
3) In cross server RvR, you no longer had grudge matches, as no one ever showed up enough to remember.
4) Making almost everything so solo friendly, no one had a reason to group up before raiding any longer.
5) Making the elite dungeons so easy that any random group could complete easily, again made it so you no longer had to create core groups of friends to allow you to progress through them.
The only social aspect left is raiding and raiding is quite time consuming, so that leaves a lot of people out of that world. While I've done that a few times, it takes time to get geared up to be able to raid, which most people won't stick around for, due to the lack of social interaction up to that point.