Osimhen is still young and has a lot of potential. Currently he has the best value on the market. If Osimhen doesn't leave now and chooses to join Napoli, I think his market value will fall over time and depending on Napoli's performance next season.
Napoli performed badly last season and they were not even in the best ranking this season let alone qualifying for European competitions, Osimhen must learn like Mbappe where every great and young player needs a lot of experience playing at many clubs, Osimhen should be able to become the best player if he is in the right team, I'm not sure if he stays next season and ends up dropping down in the standings it will definitely lower his market value, he should be able to play at PSG replacing Mbappe or play in a team from another league.
I'm not a big fan of Napoli but their performance in the previous season was very good where they were the strongest team in Serie A and won it, but since this season they have really performed very badly, I think Osimhen has to really choose his future path whether he deserves it. being at Napoli or playing in another league, I also thought he would play at PSG next season and could replace Mbappe because I think he really deserves to be there as a striker in PSG's front line.