promo matchmaking is a joke

It's been said a lot recently but I really need to vent right now. After winning four good games with average mates in a row I finally hit my promos and got a win after that and I just had the feeling that it wouldn't work out. So fast forward to the next game: We had two afks one whom picked Cassiopeia into Hecarim and just fed him to death and gave up like immediately. We lost of course. Next game I get a Jax who has an 18% winrate on him in 11 games and a Lee Sin who jumps into a fight whenever he can. Promos lost because of that. I lost my promos because of reasons i can't control in any way or form. It is just frustrating since I won my lanes easily that games and still were useless because they somehow managed to feed the enemies so bad.