So I've had a couple conversations here and it seems I have to clear out some misconceptions about feeding.
Feeding means you died, but dying doesn't mean you fed. To make it simple, you feed a champion when you die early without compensation.
When you die, you give your ennemy money, xp, and time to farm/roam freely. And that gives him an edge over other players. Like a boxer hitting with a horseshoe in his glove. If you die early and you get nothing from it, you're feeding. Your ennemy gets stronger and you don't.
If you die but you get something out of it, like a trade kill, or an objective, then that's different : your ennemy gets stronger but so does your team.
If you die in late game, that might lose the game (leaving your team 4v5 for 50 seconds), but that's not _feeding_ because the ennemy already has all the ressources he needed to fuel his growth.
Think of someone with an empty stomach and no energy : if you give him a big plate of food, you are feeding him. You are providing him with ressources to get going. But more food won't help him, he has already all the energy he needed.
It's the same thing with a veigar : you give him 4 kills before min 15, he will become super strong and kill anyone with an R. but you give him 4 more kills at min 30, it won't make him stronger.
That's why you don't compare end game deaths with early ones.