The league/division system is absolutely flawed

I win 6 games, get in to Platinum 4, win 2 more games, get to Platinum 4 43 LP, Lose one game, then win a game, and then lose 3 more games, now I get to Platinum 4 0 LP and haven't lost a game at 0 LP yet, I lose one game at 0 LP, and I'm demoted to Platinum 5, why? My MMR is good, its not like I have an MMR of a gold in Platinum division. Now I have to win 4 games just to get back in to Platinum 4, compared to losing one to get in to Platinum 5, what a joke.