Marcus was a very young freshman who wasn't ready to make the transition, and despite enormous talent, went nowhere.
Demin and Catchings (if BYU lands him) seamlessly fitting in could become the most important challenges. They have been team leaders wherever they have been so far, but at BYU it could feel more like their teammates are their coaches, some 5-6 years older. For sure they're going to adapt better than Marcus. These guys are hard workers and committed.
Jaxson Robinson was an example of a young high school phenom who didn't know BYU who came in a made it work. But Jax had a couple of years of struggle before Provo.