Can he? Yes, he has the natural talent. However, he has been unable to maximise this talent over the last few years, and unless he changes his approach (new coaching team, and willingness to step into the court) he will be no better than a regular top 40 player imo.
The rankings do not lie. He may be at a respectable #21, but he is miles off a top 10 position (1,000pts+) and will not be able to make up that ground without several decent results in the Masters and Slams. He will not be able to achieve those by standing 8 feet behind the baseline.