I also think the same as you, Conte's decision to sell Osimhen, is very unfortunate, whereas if you think about it, if Conte had paired Osimhen with Lukaku, Napoli would most likely have great ammunition for the front sector, even becoming a big threat to Serie A clubs and Napoli will be a club to watch out for in Serie A this season, but the decision that Conte has taken is a unanimous decision and it cannot be denied that he knows better about Napoli's future development.
Although this is a very unfortunate decision, I think Conte has considered this decision wisely. I think Conte wants to make Lukaku a target man in his tactics. Lukaku will be a lone striker whose job is to score goals. Osimhen is a better striker than Lukaku. He has a fantastic market value, is still young and has very good skills. However, it seems that Osimhen does not fit the strategy that Conte will implement. So far Napoli have won 2 times and hopefully they can continue the positive trend that has been achieved.
I think Napoli and Conte are not interested in Osimhen because Osimhen's wages are too high. Napoli management wants to cut their costs. This is why they will not keep Osimhen and Lukaku in the same squad. Moreover, Conte has wanted Lukaku in his squad since he took over at Napoli. Because Lukaku has played in Conte's squad in the past. And Lukaku was the best striker in Conte's squad. This is why Conte is so keen on Lukaku.
Conte is well aware of Lukaku's style of play. Lukaku is also familiar with Conte's match tactics. It is for this reason that Lukaku is likely to adapt quickly to Napoli's squad. Napoli are likely to see Lukaku perform well this season.