Why only Coman would come through their academy? Rabiot, Nkunku, Kimpembe, Ferland Mendy, Ikone, Coman, Dembélé, Edouard, Diaby, Nianzou and many others are all from their academy.Yup they have made that adjustment now, but that has not been their general operating model.
Look at these players born around the Paris area that were in the catchment area for their academy.
Mendy, Konate, Saliba, Kounde, Kanta, Nkuku, Rabio, Pogba, Coman, Mbappe, Mahrez
Only Coman can you consider came through their academy and because of the sheer amount of people who were ahead of him went to Juve on loan.
That is a stunning amount of talent to let slip through the cracks when you are the only major club in the Paris area.
Also there is no catchment area in France, it's not like the UK, so all clubs have access to all players. The amount of clubs in an area is irrelevant unless the kids for some reason want to stay around Paris which is actually sometimes not the case, they prefer to go away and focus on Football.
Paris have done a significantly better job in the last decade when it comes to scouting and developing players. They also have used most of them in the first team.