And even when all these gaps are closed, there are still going to be exceptions.
Say you're top lane, get cheesed level 1 for first blood, then the enemy laner freezes lane at their turret. You're gonna be utterly starved for cs for a while, especially if they're just better than you independent of xp/gold differences, especially if you're something like Garen with no ranged farm options or dashes.
Hell, people would even try to force somebody into that situation for kicks, once the parameters are made known. Say you need 50 cs by 20 minutes to be considered not feeding. I guarantee you, folks will use freezes and camping to utterly shut somebody out of the game and hurt their account. Hell, now that I mention it, I think I did this once solo: I was Yorick against a Nasus that was clearly not a great player, and the enemy jungler wasn't present top lane, so I actually shoved his entire lane down his throat and killed him a whole bunch of times. Poor guy had like Phage+boots at 20 minutes, and was desperately trying to hold off super minions on his nexus turrets.