We can't compare Ligue 1 and the English Premier League, because if players want to get an extraordinary experience, clearly the English Premier League is the best choice, and so does Victor Osimhen. He has abilities that can develop further, and personally I would regret it if he chose Ligue 1 for his next competition, because I think it would hinder his development a little. Not without reason, because in Ligue 1 there is no tight competition so that will make it comfortable, and when players feel comfortable then they might become lazy.
Meanwhile, in the English Premier League, competition is very tight, if players are too lazy to practice then they will be far behind other players. There you can also form a very good mentality, because in almost every match, they will face opponents who are very likely to pose a very big threat to them. So in my opinion if Osimhen wants to move, then it is better to go to the English Premier League.
Regardless of the loopholes Osimhen faced for a few weeks with Napoli, he still found so much belief in them and he'sore or less the fans' favorite too. So the news of his contract extension was definitely soothing to the team and fans too. Now it's certain that they'd keep seeing and benefiting from his unique style of football. He's being a key man at the Italian side and it was although very much unlikely for them to let him slip off their arm.
He's just got more impacts to make. Napoli themselves have seen the quality of player he is and they really don't want to let him go. It's his decision no doubt, but maybe he's just got to get experiences in a different club environment. Even though, he still has an achievement to deliver onto the team too.
Since Osimhen joined Napoli, he's been their key player and he's been doing his striking job perfectly without errors, even in times of emotional derailment from fans and the coach, he's still being able to keep his mind focused. He's in no wise the best thing that's happened to Napoli. He's the best addition to the team. Although Chelsea are having eyes on him but it's likely that Napoli won't let him slip without a very good replacement for him. His exit will place a threat to the teams performance subsequently and they may likely go back drastically.
For Chelsea, he may not be able to cope immediately, he'd need time to blend and it's likely that the Chelsea pattern may not fit him. No doubt he's got the decision to make but he's got to weigh the options too considering that Chelsea can as well give him a whole new experience to football even though they're declining currently in their performance.