PSG at the moment have an enviable squad depth, all they need is to enhance it for next season due to how expectations on them would be very high as defending champions in the champions league. Imho, Gavi is a quality player but he doesn't fit into the PSG kind of football with how prone he is to injuries he can't be reliable to be consistent in a season. What PSG needs a midfielder that is void of such injury problems and Gavi isn't that player.
Generally top players in their best skills during their career don't think much about joining PSG, unless they are French and not all the time, because PSG is playing against weak teams in a lower league comparing to English Premier League, La Liga or even Serie A. In PSG, some players feel they are doing some training games before playing UEFA Champions League.
I agree that PSG needs to reinforce their team and take on consideration injuries because it is the main problem that make a team lose their matches and their first place like Real Madrid and Bayern Munich.