It's not mental at all. Rooney's capable of subtle passes around the box, pinging crossfield passes onto a sixpence, scoring headers, volleys, near post tap-ins, or long range screamers. He has a poachers instincts but has also always been valued for his tactical discipline and hard work in deeper areas. He's clearly an unusually complete footballer. Hence so many different managers have used him in so many different positions (and been fulsome in their praise of his performances).
What's really mental is the obsessive hatred people have for him on here. There's a very good case to be made for cutting him loose, or at least relegating him to a squad player but
@Wilson Litchmore is spot on in the parallels between him and former greats in the dog days of their careers. Dog's abuse quickly becomes all warm and fuzzy once a few years have passed and nostalgia kicks in.