need to vent about placements

i ended last season bronze1 got placed in bronze after a 2-8 placement set, ok i get that this season i got 8-2 carry hard as hell. still get bronze, i was beating silvers in my placements why should i not get silver? how is that i can win 80% of my games and be in bronze. can a rioter please explain to me how this system works and how it is not flawed.