Kha'Zix Damage discrepancy

So everyone knows that assassins are designed to 1 shot someone and then gets out as soon as possible. Whether it be through combos or smashing your keyboard(KatEvolved). But the one assassin I want to talk about is Kha'Zix. Th reason being I feel like he's useless as long as the enemy knows what they're doing. NOW I will emphasize on this. Kha'zix has a mechanism in him called ISOLATION. Essentally the TL;DR version is he deals bonus damage to people who are alone, with no ally pets, minions, or allies of any kind, now he does a bunch of damage to isolated targets. But when a target is with someone or the enemy team is grouping constantly, god damn does it feel like he's useless. His damage is low, his cd for his evolved Q is 4 seconds and not 2, and in league time 2 seconds is enough time to get your fucking taxes done, have 3 children, and die. Without isolation, Kha'zix is utterly useless and the counterplay to him is so simple that anyone could figure it out quickly enough. Even when he has items like He still doesn't do enough damage to be useful. And Kha is considered a late-game assassin(because of how long it takes to evolve 1 or 2 abilities). There's a super large gap between his damage. If the target is isolated, he deals a shit ton of damage with just his Q, but if he is facing a non-isolated target he does almost no damage unless he's full build with all evolve points used.