Not gonna talk about his powerlevel, plenty of threads are already there.
This is a personal thing that could qualify as QQ (so feel free to post that as much as you like)
Its not that his ult is a KS machine, similar to garens, its that, in order for him to be super effective (darius uses ult its super effective, enemy team has fainted) he almost NEEDS to KS with ult.
I just don't like the design, Im not someone that rages at people for KSing, and i understand that dariuses dont do it maliciously, I just don't like the mechanic for ult the low people so you can wreck face.
Also he seems super super strong (darius op qq) there i said it.