Check how many times Aguero has managed 30 games in a season for us as Salah has played 33 and make a comparison. Not knocking Aguero because he is superb just highlighting the extraordinary feat Salah has achieved.
The problem is that not only does Sergio miss games, he's often slow to recover when he does go out. Christ, that car accident put him out for only 2 games in September/October, but he didn't get his form and rhythm back until January.