A 4.0 should be able to hit heavy topspin looper rally balls whenever he wants, and be able to flatten it out some for a faster moving forcing ball when needed.
Just like a serve, he should be able to hit either a flat fast serve that bounces around thigh high at the backboard and also spin a serve IN 98% of the time with a high bounce for his second serve.
And on the backhand side, a 4.0 also needs a sliced defensive/neutralizer stroke in addition to his topspin passing shot stroke.
The only shot you hit ONE way is a volley. That way is always with a little backspin for height and depth control.
Even you overheads need a flat fast one AND a sidespin slower safer one.