When a solo laner or a jungler dominates an early game and goes on to carry, i always just feel they played pretty well and went on to win. But for some reason when bot goes 0/6 and they have a fed vayne running around it feels so much worse. Its like i just expect more because theres 2 people down there? I dont know really. But for some reason id rather lose to any other role then some 20 kill lucian lol.
Because there is no way to outplay an ADC besides killing him
You can't dodge his AA, and if you do (by standing out of range) eventually he just takes your nexus
I dont know what game you're playing where you actually lose to an "fed adc".
A fed top/mid/jungler/anything > fed adc.
Adcs are free 300g bags for the other roles right now, a 10-0 jinx will get destroyed any time of the day by a 0-1 irelia as soon a she completes trinity force.
It should feel bad especially if you are mid or jungle because you have the entire early (and probably mid game if you're doing half decent) to shit on them and make sure they don't get fed.
Simple answer? Other damage spikes on other types of champs generally have a gradual increase in damage. Adcs and the Crit pathing generally receive a damage DOUBLING, which opponents are unprepared for.
Because tying a group of champions' main and sometimes only damage capability to point and click unavoidable autoattacks isn't a prime game design decision.
then because of that decision, their prime role which is DPS is balanced around their items, and when there are meta shifts and changes to the items this not only affects individual champs, but the entire class as well.
this is why crit marksmen feel like shit to play as and against, and why they universally struggle when they don't have other viable builds like on hit
/lifesteal
/penetration 
/abusive cancer
.
You touch their precious crit items and the same group of champions can go from overpowered to underpowered in a single patch without even touching them directly.
Okay, but anyone with 20 kills will carry anyway.
