Assassins, Marksmen & Mages: Is One Shooting really overpowered?

We all know the fear of a fed , Dark Harvest with or I know that being killed in the space of 2 frames is not nice, but, is it really overpowered? I believe not, most champions that do one shot can be killed the same way, is a endless loop. is actually squishy (unless you build him kinda tank, in which case you can't one shot) is squishy (there is no tank Draven, being honest) he can only do it when fed (unless you are or and have your back completely exposed)

I have no issue with any champion that actually is like this, Lots of Damage in exchange of a Small HP Pool This is not wrong, and Im perfectly fine with this, I DO HAVE AN ISSUE, with Juggernauts and Bruisers making people disappear ( ) I play Jax, (Only on Ranked tho) why is a champion like Jax allowed to one shot? My KDA was 28/5/6 (A little fed) and I was able to One Shot Kayn with a Single W, but the thing is, I didn't even go AD, got (I know' Sterak's passive, I literally rather the shield) , I even had the tank jungle item (It's better than the Attack Speed one on Jax) the only damage items I had on were and so, why was I one shoting people? I don't know. The same applies to why is a_** TANK**_ (Don't you dare to tell me he is not tanky) allowed to pop some minions (like everyone does btw) and then _whoops! _ my Q landed on your ADC, oh! Im sorry, now it landed on your Mid Laner, Hey! you are actually doing some damage to me, guess I'll just ult!

In conclusion, my point is, keep it balanced: +Damage = -HP? Great! () -Damage = +HP? Excellent! () +HP = +Damage? uh... () ++HP = ++Damage? NO ()

Disclaimer: (Whenever Nasus uses his ultimate his HP increases by 300/450/600 and his Armor and MR by 15/45/55, but on top of this, his Q has reduced cooldown, so you basically have a tanky champion, but the tanky champion one shots people, also Armor and MR keep increasing over the time his ultimate is active)