The one game he played this season he played well, made a great run that would've counted as a goal if it weren't incorrectly called offside.
He's shown that he has the ability in those 8 games under Van Gaal and in Southampton to be very very good, I'd much rather play someone who can reach high levels than those that are distinctly average. All the top sides have technical, pacey fullbacks, instead we have one that doesn't do anything (Darmian), one that's good on the ball but has no pace (Blind), and one that cuts back and crosses into the stands 9/10 times (Young, though a bit harsh as that was just last match, I do like Young at LB).
Something like 'trying' is incredibly subjective, I saw enough effort in the one actual match that he's played this season. I'm also incredibly hesitant to take on board the judgement of Mourinho on technical players given his similar assesements on trying/ off the ball work on De Bruyne, Mata, Lukaku etc. Maybe it's true but at least play him in these dross matches and then judge him.