To be honest, I've played with/against darius several times, and he seems fine to me. Generally, when Darius kills someone in a teamfight on my side, that same someone was ABOUT to kill one/more of our team with one of their own powerful abilities. Like once, a semi low hp Fiddle Crowstormed into our team, all of whom were pretty low. We all focused, and I almost got killed due to my low HP... then Darius cut him down, and the rest of our team yells "KS!" when I say "Thanks, dude!"
So yeah, I've never had an issue with Darius.