I think demar really needs to be measured as a SF going forward, because I think that's going to be his position in most games. It's a bit of a delicate distinction, but I've noticed that in the last couple of months, teams are more and more defending him with 3s and he's more and more defending 3s too.
I don't think demar will ever be a strong defender at the 2, but he does have a shot at being a solid one as a 3. Ross may need another 2 years until he's ready to take on guys like carmelo or lebron or even JJ. Until that time, it will probably be demar's job and with some added strength this off-season, he may turn out a dependable defender.