Well really ill take anyone over kha that isn't elise.
I'd agree with that, but it's nothing really to do with Kha; I've seen like one good Kha'Zix jungle in my personal games, and that was when he was super OP. I don't think there are many jungle Kha'Zixs at my elo that actually know how to play him; that's why I don't like seeing him in my game. I would say the same thing about Lee Sin or LeBlanc or Zed; I don't trust my teammates to know how to play them.
You cant fight for objectives, you cant outsmite the enemy jungler.
Again, that applies to most junglers in the game. I get the general gist of what you're saying, where most of what Kha'Zix brings to the game is damage/assassination ability where bruisers and tanks bring more CC, and if he gets behind, he's pretty lackluster, but that would be the case for any healthy assassin. Assassins are meant to be high risk, high reward. If you want to play a safe pick, you should be playing a different champion.
The reason I say he's fine is if he's even, he'll do fine in the game, and if he's ahead, he just snowballs super hard. I've seen this happen numerous times in Challenger games vs some of the best players in the region, with a player that actually knows how to play and how to build him. Side-note; Kha'Zix doesn't even have to build full damage for him to be able to one-shot people; same is true for Rengar; if they combo their abilities properly they can delete a squishy with like 2-3 damage items (including their jungle item).