I don't believe Lukaku is a better player than Osimhen currently. Osimhen gives you more than just goals, he plays with the team. He joins in the build up of the attack, he's also a hard worker. Lukaku was part of the reason Belgium got eliminated in the Euros. He waste too any balls. Any ball that gets to his feet gets wasted. I agree he knows how to score goals, but if he's not in a goal scoring position he can't do anything with the ball. We saw how instrumental Osimhen was for Nigeria in their afcon, I can't say the same for Lukaku in the Euros. Osimhen may not be an elite striker that can beat players and score, but he can score and he's currently better than Lukaku.
I believe Napoli have already told Conte they plan if selling Osimhen that's why he doesn't count on him. If Lukaku was that good Chelsea would have kept him after buying him for 100 million.
I believe the reason Napoli is finding it hard to sell Osimhen is because of the price tag they put on him. Nobody would buy Osimhen for 150 million. They can sell for about 80-90 million max. Chelsea are interested in a direct swap deal but Napoli wants more more. The same thing that made PSG pull out of the sea. I think it's looking like Osimhen will remain at Napoli.
For now yeah Lukaku and osimhen are on different levels, I agree that osimhen looks better but we also have to compare the age of these two players which has an impact on their performance. Romelu Lukaku will enter retirement in the next 2-3 seasons while Victor Osimhen still has a career at the age of 25 so it is not an exaggeration if we say Osimhen is better. Napoli are targeting Lukaku as a replacement for Osimhen because he has enough experience in Serie A and is also cheaper it means Napoli get players and money, sometimes clubs have to take strange decisions when they need enough funds well this is the situation that Napoli is experiencing, unfortunately the negotiations did not go as expected..