A little help with Kha'Zix?

I recently played a game where Kha'Zix went top vs our Rumble, and he dominated the lane. We tried to focus him late game, but he had a lot of healing capability, as well as a GA. He was able to stand in the center of a team fight with only one defensive item, and tank through all of our damage. As an assassin, I'm not quite sure that this is his intended purpose. I don't think he should be able to carry a team fight like that. Look at Zed (Escapes the team fight with his ult), Shaco (Q away, little devil), Talon (Lol nope), or Kassadin (Ult in ult out). All of those assassins HAVE to get away to survive the fight. They can't just sit there and take it all. Kha'Zix is a lot of fun, and excels as an assassin.. But he also does very very well as a regular, tanky, fighter. Just a thought..

Also, I noticed something else about his Void Spike.. It was my understanding that the spike had to hit you to actually proc. I was at the very end of his spike range as Varus, and stood between the two spikes. I still got damaged without them actually touching my hitbox. Does it affect the entire cone, or was this just a weird misplacement? I was sure I was between both, especially since neither rocket (he had the mecha skin) exploded, but I still died from it.