It's not that bad.
The basic issue is that when botlane gets fed, it gets really fed.
But if you watch LCS, usually it's actually about half bot and half mid putting out the real serious damage in a lot of games. They share the team with 2 tanks and a hybrid or utility character as a general rule. Others you might even have 3 or 4 damage dealers.
It's always frustrating to be able to do nothing against the unkillable fed botlane, but I think how to fix it without making ADCs feel bad to play is a tough issue. I don't think the role is easy now! When I ADC I'm always amazed by how tough pure marksmen have it in the early game as it is, and you're only ridiculously dangerous when fed. An underfed ADC is a useless snack to this day and right now, as we speak there are millions of ADCs in games out there right now who didn't get the 3-4 kills needed to snowball and are having a lousy day.
Maybe Riot buffs early damage levels or health or something on pure marksmen in exchange for a harder late game falloff?