Faulty ranking system

I just won 8 games in a row only lost 2 games and I did very good how is it possible that I only get platinum that is -Yoinking!- -Yoink- should of atleast been diamond this is the second -Yoinking!- time I get -Yoink-, my friend in same lobby as me gets better rank and I’m carrying him how the -Yoink- does that work trash -Yoink- game if you ask me