PSG team could not use a player like Lionel Messi well. One of the reasons for this is that the coach of the team does not have enough knowledge of how to use a player like Lionel Messi.
It's not PSG's fault but it's galtier. PSG was just recruiting him to the club while galtier was the guy who has responsibility to use the resources that are available on PSG.
Galtier thought that he couldn't unlock Messi's potential because he did not have the right strategy for him. It's very wrong to blame PSG caused by galtier was fully responsible to the squad last season.
In fact, galtier was always changing the strategy because he was trying so hard to discover the right strategy for MNM.
MNM was trio between messi neymar and mbappe. That's also the main reason why PSG has sacked him from being a coach.