He's not "shit", but he is not good enough to start for a club with aspirations like Barcelona, that has been well established. The only issue is on our national team that with Adrien just coming back from injury, Renato Sanches not playing at Bayern, and Moutinho getting older we need a CM to partner William to let the front 4 roam with Joao Mario/Ronaldo/A.Silva/ B.Silva or Nani Is Joao Mario good enough to play box to box? I'm not sure...he's more a deep laying playmaker, but I'd try it against average teams to test it out until a great CM option becomes available.
The good thing is that we have options both young and old even though there is no one who at the moment is making that spot his own.