The thing with TBC is that not only were elements of it just godawful (Kael, Illidan, the draenei retcon, Vashj), not only did they inflict long-term damage on the playable factions (The blood elves being added and then rewritten by the end, the aforementioned draenei retcon), but it was also extremely poorly told. Things like the arakkoa or the Mag'har only actually became interesting in future expansions and it was the first time the game went full tilt into science fiction and killed off huge figures, consigning the story to its direction of constant escalation that it only escaped for a little while in Mists. Couple that with it being atrociously told, with major character turns and motivations explained in novels you had to pay for ten years later and you have the worst lore in an expansion. For the competitors:
WoD had no consequences whatsoever except for the two people that cared about Maraad and fleshed out the orcs beyond being the identical noblesavage stereotypes without clan differentiation that the WC3 retcon ages back had produced. The main story was total shit on a crusty roll, but nothing really came of it except Gul'dan and if you don't like it you can basically pretend it didn't happen. Mists is the best told of all expansions, damning by faint praise though that may be, and has some great world building, but had godawful consequences. BFA is marginally better told than TBC if only because the tie-in materials aren't released ten years after the fact, but while its consequences will be far, far worse for the playable races, irreparably so, it at least has some elements that stand on their own like the Zandalari and Kul Tiras. I dare you to remember what happened in a single zone of TBC, and going on about how naga are stealing water to do something (???) doesn't count.