many of them seem to struggle for a while in the league before carving out a solid role
This description could hold true for pretty much any young player developing in the NBA. Guys who become good role players rarely do so immediately when they come into the league.
That's true, but I think players from some other schools -- Duke, for example -- have a clearer idea of what their best role is in a team context.
Guys like Patrick Patterson, Terrence Jones, Brandon Knight, MKG ... lots of raw talent, but their intangibles as team players, i.e. their ability to contribute to wins apart from putting up numbers, seems lesser to me compared to guys like, say, Mason Plumlee, Gerald Henderson, or even Kyle Singler.