Why are certain mains much higher elo than others?

In my opinion, certain champions that's are mastered have a much higher rate of getting you into a higher elo. For example, all the mains from what I can see are actually gold or above. Riven mains also seem to be pretty high. Certain roles also seem to be easier. As a support, all you need to do is to help your adc and help them carry. In a way, your just having someone carry you then. I've also noticed that higher elo games seem to have far less skirmishes. In a bronze game, the would go in senselessly and most likely get 1 or 2 kills. At maybe challenger level, they don't fight as much but get Penta kills. Give me your opinions on how different mains and role and habits work for higher elos