I do think that's a problem with him, and more what I meant in my post... I see that I wrote "he's incredible in game, but has fallen off late," and I'm not really sure how that came out, aside from it seeming to be 1:30am blarghlehargle--- more accurately, I wanted to say something more like "He's incredible in lane, but seems to fall off late game."
And I think what you say pretty much sums up the problem with him. He lanes very well, due both to his kit and because he has "Kayle-syndrome," where no one really knows how to play against him that well right now, but late game, he has trouble finding his place in a fight and making himself effective during the entire teamfight.
I can completely imagine why some-most melee AD solo toppers could have problems with voli. That bite is insanely good.
But it's also a question of winning that first trade that makes them fall behind.