It's a win-win situation for PSG, they didn't really lose Mbappe because Osimhen is also a high tier striker, so he can replace Mbappe's position and shine on there because Ligue 1 is a farmers league. Goncalo will back to Benfica in the middle of the year, PSG probably know Mbappe will leave them and they will sign Osimhen, that's why Goncalo is a loan.
Well it's not really a big achievement if Osimhen can perform in PSG because he must able to perform. While in Premier League there are many tough teams, so it's not a bad thing if he can't score a goal in every match.
If Osimhen chooses a safe position, the option of moving to PSG is the right choice, because the competition there is not as competitive as in the Premier League. From a financial perspective, PSG has the ability to pay off Osimhen release clause which is not cheap, but several Premier League clubs also have the same financial strength. Playing in the Champions League every season is Osimhem consideration. Chelsea, who are reportedly interested in the Napoli striker, seem to have lost in his efforts to hunt for autographs before the transfer window opens, if Osimhen wants to play in European competitions every season.