The buffs are nice but they don't really get to his real problem which is that kha'zix is too squishy for how much damage he is able to put out right now. If you build damage you get one shot in a fight and you're useless unless you can 100% the opponent (unlikely since they nerfed him because any champ that can 100% is not a healthy champ). If you build tanky you are getting away from his assassin roots so there's not point in playing him because of all the much stronger juggernaut choices and also your claws turn into wet noodles.
Not to mention kha is a late game champ which causes a whole other slew of problems. First that his jungle clear is awful right now so you can't farm to late game with a few occasional ganks and expect to get items fast enough. He is entirely dependent on getting LOTs of successful ganks which is particularly hard since it is damn near impossible to dive a tower pre-evolved wings without dying. So unless the enemy team pushes hard and is very squishy, ganking is either too dangerous or ineffective. Also the tank items and tank champions all scale much better than him, so unless you snowball enough get your damage up more than they get their tankiness up, you will lose in the end.
Any attempt to take out a carry is suicide in a team fight unless your team is tanky enough to initiate hard, survive for a few seconds, and get some CC on your target so you can last hit. Otherwise you jump in, do your combo, find that you dont do enough damage to get your reset, hit r and hope an aoe spell doesn't kill you, then die once your visible again. And that's if you're lucky enough to not get any hard CC on you.
So in all phases at the game kha is at a considerable disadvantage. It's just sad that such a cool and fun champ with an awesome kit offers no real benefits that you can't get from stronger champs. For the time being Im just going to stick with my voli jungle who for some reason is able to do more damage than kha, survive ridiculously longer, and offer more utility.
Sorry for the rant but I could go on even longer haha. I've been trying to get kha to work since post season with no real success compared to my other champs.