Osimhen was an option for PSG even in the last season. I think Osimhen could have even better performance in the last season when he was in the better form but now PSG knows they can't expect to see a miracle from this player but he can have a good performance like two years ago and he can be out of the good form like last season. I think there can be better options for PSG than Osimhen and they should not be worried and run for finding a replacement for Mbappe because Osimhen and Mbappe are not at the same level at all.
Your comparison isn't sounding solid, I know I'm the last season, towards the end of the league osimhen's performance did dropped and that too has affected his price but on a second taught it's possible there were factors that led to that which if taken care of he would do better, at PSG those factors that led to his poor performance may not be there but PSG still isn't a fit for him, his career may not do so well in PSG.
At the moment PSG isn't prioritizing getting him into the squad and he is yet to even show any interest in PSG as an option for his move, there were rumors of an interest in him by PSG last season before the end of the season but the deal didn't pull through and even now it's not looking like one that they would want to revisit again. Away from PSg, in other teams if osimhen gets and opportunity he's still gat some good potential.
Personally I think some people are becoming bias with the performance of Victor osimhen last season, osimhen's team Napoli lost form last season that alone affected the performance of all the players because as they couldn't win matches anymore and the goal scoring abilities of the player couldn't be seen again because nothing was working in the team. PSG were interested with him but then Napoli wasn't interested in letting him go even with the offer but since they appear not to be interested in the deal it is better goes where he will supported and appreciated instead of going into a team that won't respect your decisions.