That's not how it works I think. A lot of players benefit from the team around them. You can see that Ronaldo is the best scorer in the Saudi Professional League, but it is not as if he was a god who is scoring 70 goals in a season. There are a few good players at Galatasaray Istanbul, but it is probably not the same level as when he had the privilege to play for the top notch Napoli team 1.5 years ago. A striker like Osimhen needs assistance. He is not the type of player that takes the ball and goes for it 1 vs. 5. He needs the perfect pass or cross ball. I still think he should do quite well given his quality, but I imagine that adapting to the Turkish league may be a bit different compared to adapting to some European leagues.
A team can help someone to achieve their best career and it is a collaboration that is done as a collective work in football. Ronaldo became a player who has many trophies and individual achievements because he has teammates who are in line with him and vice versa with Messi. The role of teammates is quite large because without them it would be impossible for both players to have achieved everything in football. Collective play is very much needed and each other will encourage each other to achieve whatever is targeted by the club or in terms of each player's individual career.
In terms of adaptation, I think Osimhen will not have difficulty because in the club there are several European players who play there so they understand how European football is and now the Turkish league has also adopted a game like Europe. But if asked to be completely like the game in Europe, maybe this cannot be fully implemented and Osimhen must understand that as an effort to adapt.
But there are still huge differences between players in regards to their dependency on the rest of the team. Messi and Ronaldo were able to score goals for themselves due to their superior dribblings and ball control in general. Speed and force and agility were the things that set Ronaldo and Messi apart from the rest and that gave them the opportunities to score goals without the team assisting them.
Osimhen on the other hand is not like Messi or Ronaldo. He is good when he has the ball and he is definitely agile and his movements are great, but he is not a player who can take on several opponents at once and then successfully finish off the attack. He is more the player who is waiting for a good ball to reach him and then make the best out of it, that could be a perfect pass or a cross ball. If the quality of the players around a striker drops significantly out of a sudden, it is far less likely that the striker can produce the same number of goals as he did before. I see this as a test for Osimhen although it should be kept in mind that the whole level of the Turkish league is far lower in general. You can't compare the Turkish league to Serie A, let alone to La Liga or the Premier League.
In my opinion Osimhen has now wasted valuable time to further build his profile as a top star in Europe. Even when he now scores 30 goals in Turkey, it won't be the same as scoring 30 goals in Serie A. God bless he didn't choose to go to Saudi Arabia at his young age. I wouldn't have been surprised if he did.
The most likely scenario - that is my guess - is that if Osimhen plays well for Galatasaray Istanbul, there will be a few big clubs watching out for him during the winter transfer period. Since he has a clause in his contract that he can leave Turkey if the interested club is willing to pay the fixed fee, I guess he will probably be gone by January. There will definitely be at least one club trying to improve their own team due to whatever reasons. Could be their own strikers failing or injuries.