Pre-rework was kinda bland.
He was an immobile champion with short ranged abilities and no CC.
Almost every other champion have one of these attributes: Mobility, Range, or CC.
Pre-rework
, one of the easily kited champions in League had a reliable slow cleanse and MS boost.
, another immobile champion, can perma-slow a target if he landed his cleavers and has a MS boost on his ultimate.
Mordekaiser is seemingly left entirely out of the water because his Ghost ultimate is so powerful. It potentially turns a 5 v 5 to a 6 v 4.
Old Mordekaiser was boring to play, and boring to play against. His abilities are all basically targeted, if you get in to his range, he kills you, if you don't he can't kill you. Fighting him is basically a stat check,
However, new Morde really isn't better.
Rather than giving him something so he can be viable no matter what, Riot made him even more gimmicky.
First, his EXP gimmick means that he essentially win lanes by going even.
His W healing gives unparalleled sustain in lane.
His Q gimmick can one shot most champions early on, and perhaps even late game. However, if he mis-use it, he has no kill potential until it is back up.
His ultimate Ghost gimmick is even more powerful now that he can ghost the dragon.
Fighting new Mordekaiser is a guaranteed loss unless you can bait out his OP abilities. Otherwise, he will 100-0 you with R, Flash, third Q.
But if we nerf his Q, exp bonus, or R, he becomes suddenly useless. The rest of his kit still is in the same spot as before the rework.
It is hard to balance new Mord. If he gets close to a ranged champion right now, he will win almost 100% of the time. The times he loses the fight is when he can't get to his target and kill him/her in one hit.
However, if you remove or tone down his 900% AP/AD scaling, suddenly getting close to someone is a lot more risky.