Rudy Gay and Quincy Miller are, in my opinion, the type of player you referred to as being able to create their own shot of which you felt teams needed at least 2 of.
I would not want DeMar playing at the SF unless it was a favourable matchup. Looking around the league most SF's are 6'7/6'8 and 225-240 - there are exceptions but that appears to be the norm.
Agreed, I don't think DeMar at SF is a good idea from a defensive perspective. I find that DeMar has enough trouble as it is checking guys his own size. Things will only get worse when you match him up against bigger, stronger players, who also have legitimate post-up games.