There's always been this belief that even if something is well recieved (see: expansive world zones in Vanilla, Suramar, Wotlk Glyph system, Ulduar hard modes, WoD world treasure) it must be changed to keep the game 'fresh'. Same with class design. WoW should be firing on all cylinders in terms of its design at this point but because of the massive and usually unneeded changes we keep getting haphazard outcomes and sloppy results. Just think of all those times a class has played brilliantly one expansion, only to turn into a complete turd in the next expansion.
It's defensive design philosophy, and it's almost resentful of anything that worked well previously. WoW devs have always argued that massive change each expac keeps the game from dying, but I would argue that poor design outcomes have wounded the game more than anything else.
And don't get me started on the game's story. No department in WoW is more insular, defensive and resistant to feedback than the writing team.