Atleast stop giving the player worse teammates when they have too high of a winrate, make the person who has a high winrate play against AND with people of an equal to or higher elo and see if they can keep up.
Have players with a poor winrate play with and against people of their own elo or slightly lower. (higher winrate teammates)
This doesn't force 50% winrate nearly as hard since a team is only as strong as its weakest link, your job is to not be that weakest link and do your best.
And its easier for someone to have to carry a tilted person who is higher elo than someone who is more likely to not have any idea what they are doing and how they should help the team.