Why Morde was Reworked, and Why Riot Will Not Revert Him
Honestly, it hit me when I saw all the Yasuo QQ on the forums: Yasuo is very fun to play as for his mains, but for opponents facing him he can be a very unfun champion to face against.
Pre-rework Mordekaiser had the same problem.
Between being able to put his Creeping Death on a minion advancing the lane, his Mace of Spades and his Siphon of Destruction for shield, and his Siphon also letting him poke, and you find that he is very difficult to balance, but even moreso: he is not fun for anyone who doesn't directly shut him down to face.
Mordekaiser was a simple and straightfoward champion - often criticized as being extremely simple with little skillcap - and he was known for being a 'noobstomper' for a very good reason: you weren't going to be able to do well against Mordekaiser if you couldn't understand his Passive, Iron Man, and how all his abilities fed into it when he did damage, especially to you.
Actually, while their kits behaved differently, pre-rework Mordekaiser and Yasuo shared similar things that made them frustrating: they had ways to make trading and poking them hell for you, Morderkaiser with his Siphon to poke and shield and Creeping Death to negate poke, and Yasuo with his Steel Tempest to poke and his flow and Wind Wall to... negate poke.
I seriously just realized that.
Granted, Mordekaiser is as immobile as a turret being dragged by a bunch of yordles, and Yasuo couldn't be more mobile if he learned from Riven, but their kits make them frustrating to play against for the same basis: trying to deal with them only creates a headache in trying to win lane against them when they can invalidate the majority of things you can do.
Honestly, current Mordekaiser isn't that much better, he was just moved to a lane where people could trade with him meaningfully.