How about not a factor at all?
Bad decision, no dispute from basically anyone. Doesn’t change the behavior of either one.
Ultimately yes, but that was Marvel’s call; besides, what happened to the notion that Jean would be better off without the Phoenix? Not that you’ve asserted that, but still.
Jean’s presence wouldn’t have changed the things that led to Scott taking the lead; she would either have stood with him or been the opposition in a split, but Scott’s trajectory stays basically the same.