The reason i hopped on the ''nerf adc'' bandwagon.
Before then, i never really noticed how the adc class was prevalent, until i started playing Leblanc quite recently, which is my first assassin ever, and probably my most ''aggressive'' champion. Since then i realized how difficult it is to deal with adcs. I'm perfectly fine with adcs being fine when they're alongside their teammates or support, diving in a 1v2 is a huge risk and should be in favor of the duo. But when i can't burst down an adc in a 1v1???
Equally fed, i just can't kill a Tristana/Twitch/Kog in a 1v1, they can kill me before my passive procs (which is as little as 1,5 seconds) they start being impossible to solo as soon as they complete their second or third big item. Unless i've got a lead over them, or they have a unlucky no-crit streak, i just can't kill them before getting killed. I might be able to chunk them down, but they'll lifesteal back just fine, while i'm being forced to back (if not dead) after getting right-ckicked on.
If it's already so hard to kill an adc in a 1v1, it becomes almost impossible in a teamfight where they have peel and shields to protect them.
Assassins are supposed to punish poor positionning, being alone and squishy should be enough to spell a death sentence to them in mid/late game.