Is it possible that you're losing more often in the games you aren't playing with your friends, and winning more often in the games you are playing with your friends? Then they could have a higher winrate despite you sometimes playing together.
Also, like... if the game is keeping you "stuck", just keep improving until you can trash the lobbies. Either your skill rank will improve, or you can come back here with a 60% winrate and 16 game winstreak, and have much better odds at catching dev attention.