I figured out why having the worst player on team matter more than the best player is so frustrating
It's not that the matchmaking is any shittier than it was before, nothing has changed in the matchmaking as far as I know. It's that once someone on the enemy team is fed enough (and it doesn't take much, usually a 3 kill lead is enough) you CANNOT outplay them (barring a VAST differential in skill like Challenger vs Bronze) they have to outplay THEMSELVES. It doesn't matter if they just picked up their champ that day or if they make huge mistakes, or if you cc them to oblivion; they will stomp you once they have enough of a lead, hell they will stomp you even if you are more skilled and bring 2 friends if they have enough of a lead. And this all can happen 5 minutes before a surrender is possible, and it has to be unanimous.
Bottom line, Riot has to remove all the snowball runes, items, mechanics, w/e contributes to snowballing from the game, and make it so SKILL matters, not just getting lucky and getting the snowballing rolling into unstoppable death machine. Having a lead shouldn't mean you can coast to victory with zero effort, you should still have to play smart and not have the ability to get away with HUGE errors.