Now that we have some history with Barner to go by, it seems pretty clear to me that he wasn't acquired primarily as a punt-returner, but as a backup RB (with his punt return experience being a bonus). As an RB, he appears to be very good about following his blocking and not going to the ground at first contact. He also seems pretty solid in backfield pass-pro. His YPA (so far in limited usage) hasn't been much below Bolden's. There's really not much more you can ask for from a guy in the (very necessary) backup RB role.
WRT Patterson being used ahead of Barner, it seems pretty clear that it's a case of McD experimenting with more ways of getting the ball into the hands of a playmaker. For example:
Patterson's first 7 games this season:
... 15 tgts, 7 carries = 22 total opportunities = 150 yds (21 yds/game) and 2 TDs
Patterson's last two games (avg 17.5% of O-snaps):
... 1 tgt, 21 carries = 22 total opportunities = 106 yds (53 yds/game) and 1 TD
More significantly ...
Patterson's first 3 games after Edelman's return (avg 9.6% of O-snaps):
... 3 tgts, 2 carries = 5 total opportunities = 31 yds (10 yds/game) and 1 TD