You’re asking for something that game has spent the last 13 or so years doing anyway. Your only real complaint is that flying happened along the way, and yeah I stopped playing cata prepatch because flying in azeroth was too much for me.
The people clearing BWL had MC gear. The people clearing AQ40 had BWL gear. The people clearing Naxx had AQ40 gear. Throughout all of WoW, every tier remained relevant for choice pieces, the BiS tanking sword in the game dropped from MC. That was a perfect way to develop raid content because nothing became obsolete due to the next tier. TBC copied this in a big way with t4 being as much worth a guild’s time as t6. It’s bizarre to enjoy classic raiding and PvE content but reject TBC at the same time. It wasn’t until WotLK that each tier nullified the previous.