Are assasins way too unhealthy ?

I actually not that good in the game , however i still have noticed that assasins are wayy too unhealthy right now as someone who played alot of ( currently level 7 and 6 with them ) is it really fair to delete target under 1 second ? they force immobile mages to build zhonyas even if it ruin their build , because of the lack of counterplay assasins does have cough cough talon and zed and fizz , sure they got some nerfs recently but i think it is frustrating to play against them especially if you are an adc main . kha zix is one of the best junglers right now for me , since the last buffs he got his play rate have increased dramatically , i remember him being urgotten in s5 and s4
Rengar thunder cat build does insane dmg , and this is why people spam tanks , just to not get deleted by this mofos lb point click double Q gg ...... such skill much brain
i am not telling that assasins shouldnt be doing damages , but i think they lack counterplay and their damage is so easy to pull off .