It doesnt matter what your rating is and whether its higher or lower than your teammates. Your GM will basically never trade your "star" teammate no matter how good you are or how much he sucks.
They also changed the trade logic in My Career. It used to be that you would be traded for players of similar rating in current gen. Like if youre a 90 ovr and get traded to the Knicks then theyre trading Melo or something. But I guess that pissed a lot of people off who wanted to play with star teammates only to see them traded away. So now basically regardless of your rating you will not be traded for a star teammate. Thats what I gathered from seeing youtube commentators and my personal trade experiences. Trades usually result in you being traded for a low rated player and draft picks.