I agree that Osimhen is a quality player, but his value is so expensive that some of Europe's top teams are reluctant to spend much money on him. Chelsea could try to bring in Osimhen in the next transfer window if Osimhen is ready to leave Napoli. But if that happens then I think Napoli will not be able to compete closely in Serie A.
Of course Osimhen is a complete striker, he is tall, runs fast, is able to open up space, can provide assists, his dribbling and finishing are very good. He is also not the type of lazy striker who just waits for feedback. Napoli deliberately set a high price so that other teams would think long and hard about bringing him in, this proves that Napoli don't want to lose him.
Napoli have changed and their performance is no longer the same as last season. I wouldn't consider Napoli as one of the title contenders this season if they didn't finish second during the first half of the season, so for me Milan and Inter would likely be the two best favorites to win it.
Since being coached by coach Rudi, Napoli's game has not been as strong as last season. Napoli this season will have difficulty defending their title and even finishing in second place will be difficult for them. My prediction is that even though Napoli are in the top four, they will struggle this season.