I tend to just think he needs a certain type of management, and other more personable managers would get a lot more out of him. I know that's probably not a popular thing to say, in the current climate of people getting annoyed by 'highly strung, prima donna footballers' etc, but the reality of life is that some people don't respond to Mourinho type management and it doesn't make them worse or weaker, it's just different personality types.
Personally, I'd hate to be managed by a man like Mourinho and I think the fault lies with him much more than Shaw. He's basically humiliated him a few times now.
Whilst I agree Mourinho's style doesn't work for everyone he's also played under Van Gaal too and approaching four years at the club. During that time if his form was even half decent he'd be playing every week such has been the level of competition they've had at left back. As it is they've played a right back (Darmian), a utility player with no pace (Blind), a centre half (Rojo) and a right footed winger (Young) over him. He's been overweight, quite visibly unfit and had his attitude questioned by virtually everyone involved with him.
If you could get him for a bargain, which is unlikely, then you'd say he might be worth a punt but I'm sure there are better options out there that are more professional.