MoP class design was heavily overrated. Everyone had a lot of stuff but it was overpacked in my eyes.
I for sure dont miss things like Second Win(d) on Warriors, completly broken Rogues and Mages especially with Alter Time, my Ret being absolutely useless outside of Wings, BM Hunters stomping everyone into the ground with Stampede and Kill Command Spam, and the crappy legendary cloak everywhere. PvP wise speaking.
And WW Monks being pure garbage at release and then stomping everything into the ground in the later patches with being able to do everything, the burst of a ret, the CC of a rogue, the sustain of a healer and the kiting of a druid. Yeah, no, not fun at all now that I think back of it.
Still love seeing all the typical PvP crybabies keep on QQing about class design and balance instead of finally unsubbing for good, with some of them doing this since the beginning of BfA and even Legion.
Oh how Blizzard has these poor people addicted.
The coolest part about MoP was Lei Shen and Challenge Mode, definitely not class design. Just because it was better than it is now it doesnt make it instantly good.
Thing is, this Game could be really really good right now if Classes would be more in depth. I can only imagine the fun I would have with better talents and a few more spells on my DH in M+.