1. Leaving/AFKing/identified inting person loses 80% of the LP loss for the match. This fixes the zero sum problem, while also leaving the responsibility of the match result on the person that determined the match result. Not only would this make matchmaking MUCH less random / unfair, it would also disincentivize trolls and AFKers, since they'd only be hurting themselves. For people that have connection issues, it's still their decision to play ranked, and a decision that their 4 other team mates didn't get to participate in, so why should their team mates take 80% of the blame for their decision?
2. Gate the matchmaking based on people's actual rank. Regardless of whatever batshit results the MMR system is giving them, don't let games be put together where four Gold 4s are put against 1 Gold, 2 Silvers and 3 Bronzes. Regardless of what the MMR says, that game will 100% of the time be a blowout, and allowing it provides absolutely no value to anyone.
3. Rather than requiring a majority to choose to remake in the first 3 minutes, the game should require a majority to choose to continue. The default of the game isn't a 4v5, so why should the default of the remake vote be? Also, absolutely nothing is more tilting than being forced to play a 4v5 during your promos because your teammates decided to troll during the remake vote
4. If people win a 4v5, they should get 20% more LP (splitting the LP of their AFK teammate). I hold this truth to be self-evident.