I don't even think a vote was necessary, Xavier should have just said that Colossus was the new member; case closed. Xavier and Magneto appointed the others to sit on the council, no vote was required for them and quite frankly what qualifications does one need to sit on the council? Saying Colossus doesn't belong because he isn't an omega or to nice/naive or has no leadership skills reeks of elitism. And honestly I don't think Peter would be some mindless yes man for anyone, the Colossus from the extinction team was his own man or like when he left to join the Acolytes. He is fully capable of thinking independently for himself.