How about forcing players on ranked loss streaks to play and win a normal before they can continue?
There's zero excuse for allowing someone who is most likely detectably tilted to continue queuing for ranked and sabotaging their team mates' MMR without punishment.
This would honestly fix a lot of the coin flip games, where the losing team has someone on a loss streak who clearly said 'fuck it' and isn't trying, or borderline trolling by trying out a new champion.
In general, more steps need to be taken to try to prevent obviously one sided stomps from happening.