You are not far from the truth in this case, Napoli for some time now doesn't rely solely on a single player, this is an evidence in the departure of Osimhen who was their main man back and also Kvaratskhelia, many people thought that Napoli will fall for some time but the proved them wrong and without these two main players, they still won the league. So I totally agree with you when you said they don't rely solely on one player.
We have seen that Napoli became Serie A champions last season. But napoli's forward's performance was quite weak. They were able to win the title due to their overall gameplay being stable.
Napoli should have taken the necessary steps to strengthen their attack this season. Because the team will perform in the Champions league this season. It is not possible to perform well in the Champions league with a weak attack. because most of the team in champions league has strong squad. Napoli should not sell Osimhen. He has the ability to score 20 +. But Napoli sold Osimhen due to conflict with the management.
Napoli secured a 2- 0 victory against sassuolo in the first match. It is a good result. They played quite well. De Bruyne and McTominay scored. Anyway, it is not certain whether Napoli's attack will be able to continue such a good performance.