How did the UI suck compared to any MMO of the time? I can't even figure out what was happening in FFXI and it was a slog to do simple things. The UI was fine and was constantly changing in vanilia. Adding things that mods brought. If anything it got bloated, but it never got in the way of playing the game. The UI of the game was probably the best part, made WoW actually engaging and not overwhelming compared to other MMOS. Quest design sucked? Compared to what? The quests were fine. The biggest complaint you can say is that they were grindy and samey. But hell of a lot better then what any other game was doing and plenty of the more important ones were actually fun. And as the game got into the BC era, the quests were far more inventive. Some specs were not valid, but it's a fucking mmo. Some specs work for somethings and dont for others. There's always going to be a meta. Even in the super controlled FFXIV, some Jobs are better suited for raiding and parties will lock certain jobs out. And thats a game where there is'nt really any type of choice when it comes to personalizing your job. Traveling a nightmare? How? You walk, use your mount, or use many of the quick travel features. I'm sorry WoW was actually an open world that required you to actually travel. It wasn't press a button and quick travel to the point that made you question if you're even playing a MMO like say FFXIV. The travel was never an obstacle in that game. If anything, one of the highlights.
The game was never bad and really to argue otherwise is pretty dumb. How could such a bad game become pretty much one of of the most important games ever made. It couldn't.