I don't doubt he is committed, and I don't think he's lazy. I think he has an inconsistent attitude and when things are bad he doesn't do his part to pull us out of it. I'd still start him most games, but not to roam the opposition's back line. Look how hard Cavani worked against Spuds today. He was winning the ball deep on the left side of midfield, playing it out in a few triangles, and sprinting into the box to get on the end of things. Everyone has to do it.
If Auba doesn't want to play left wing back, then he has to take some responsibility and help bring the ball up the field. Ideas like "service" and "tracking back" are desperately outdated. It's just football.