Help me out here since I've only been watching since about 2001. But I'm having trouble thinking of anyone we've had at the wing that would be a better defender than Barnes. The only player that comes to mind is Doug Christie but he was before my time.
A quick scan of the Raptors wikipedia page and these are the names he's up against:
My memory is fuzzy on how some of these guys played but there isn't really much competition here.