Because Coman has better technique than Berardi, I watched a lot of Sassoulo games when he struggle to control the ball properly, looking like an amateur.Also Coman is much faster, Berardi is not that fast to begin with.All I saw from Berardi is that his positioning is really well thats why he scored so many goals but other stuff.... pretty weak.
Coman is pure natural talent, but in the end that doesnt mean he will become better player than Berardi but he has what it takes.