Simmons doesn't have the heart to lead a team to a title and utterly disappeared against the Celtics. Being a generational point-guard talent and having your college team barely go .500 is a sign of something amiss personality-wise. (This counts triply for Fultz, whose University of Washington team went 2-16 in conference during his one season there.)
Embiid, for all his talent, doesn't seem to have the discipline of someone like Tim Duncan. He's constantly out on the perimeter and making his trips to the basket far more complicated than they need to be.
I thought initially that Butler might get things cracking with the two talented young'uns, but he might have hit a brick wall early and started to overdo things. We'll see about the new trade, but I'm not optimistic.