I can say with complete certainty that I enjoyed Cataclysm FAR more than MoP. And Cata was waaaaaaay worse than WotLK and tBC imo.
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While it did start the casualization, it was at the complete tail end of WotLK that WoW hit it's PEAK numbers. As in WotLK very much drew in another net 2 million people following tBC which garnered pretty much the same number (the vast majority in fact started playing in vanilla WoW contrary to your claim).
WotLK did A LOT of things right to the extent that an MMO today can't launch without a feature introduced during the expansion (LFD). WotLK also happened to have by far the most active PvP scene this game has ever seen and undeniably the most balanced from s6 onwards. Raids were more accessible than ever and people were also raiding far more than they did in tBC or even now while dungeons remained just as active.