I think - like all of the litany of midfielders we've played there in this division - he looks good at fullback or wingback because the league is f***ing woeful, and he offers a lot going forward from that position.
The problem is that (like all the rest of the midfielders we've played there) he defensively isn't good enough to play there against anyone who is actually any good, and he's nowhere near consistent enough going forward to be worth his place further up the pitch. For someone who has now played plenty of games, he's also pretty stupid and never looks up.
This isn't taking anything away from the way he's done recently but he still isn't very good, he's not improved in the slightest as he's got older, and I don't think anyone would be surprised in the slightest if he went on a shocking run of form, particularly if he gets moved up the pitch now we've got two left backs approaching something like full fitness.
(edit - should add that I'd never question his attitude or commitment!)