No, it means that player mature in their game and after years of experience get better and better in in dictating play, dictating tempo and improve tactically. Especially in that role, how many young midfielders play that "quarterback" role, it comes with time.
Bakayoko is bought as a replacement for Matic, plays in the same or similar position as Matic, whether stylistically they are the 100% same players or not, Bakayoko can well prove to be a better player for them in the longrun than Matic was for them. I am not sure how you say he will never reach his level of composure as if Matic is the midfields Messi.