As someone who's ALWAYS thinking about champion niches, even though I hate both of them for what they do, I wholeheartedly agree with this.
Amumu should apply slower and more consistent CC and damage, like actually withering his targets. I'd love it if his ulti was actually a gradual slow that turned into a root over time, and if his damage had some sort of ramp-up or escalation instead of "standing next to you till you die".
His theme is so powerful and yet his gameplay is so, so bland. He plays just like Singed.
He should be turned into this thing that's maybe not SO strong for en-masse initiation and CC, but can actually be a disruption against very tanky teams over time because he "withers everything". Maybe constant slows and an ever increasing %HP damage mechanic so he slowly melts tanks.
Sej on the other hand should brute force her way into fights. Her kit is actually more interesting imo, and closer to what her theme feels like, lobbing frozen bolas and riding her war pig into the enemy team and whatnot. xD
Both of them are initiator tanks and should have some sort of gapcloser, but I think Amumu is the one that needs a bit of work to realize his fantasy. Seju is pretty much exactly a warlord who charges in ahead and freezes everyone. :D
But I'm actually more worried about Irelia, Fiora and Camille right now. They feel like 3 sides of the same coin: dueling and diving, dueling and crazy DPS, crazy DPS and diving.
Why pick Irelia over Camille and vice versa? Why pick Fiora over Camille and vice versa?