Might someone explain the MMR math for me?

So I'm 50% win rate, recently promoted, 5 game win streak, but still only gain 17~19 per win. Isn't that LP like, bottom of the barrel win rate%? Shouldn't 50% win rate be closer to 20+? I really don't understand how this game thinks I should be in silver lol at G2 being matched against mid to high Plat players.
Reportar como:
Ofensivo Spam Mau comportamento Fórum incorreto