Of course the competition between Martinez and Osimhen is still open, that's because both of them are still very likely to get additional goals in the rest of the season. A unique fact about Osimhen is that he is often caught offside where he averages 1.2 offside per game compared to Martinez's 0.4 offside per game.
both of them still have the opportunity to score more goals because this season still leaves 13 games to become the top scorer this season. besides that the statistics you provide where I am more interested in the minutes played by Osimhen because he played less time compared to Martinez in current statistics.
Indeed Inter will be the closest competitor for Napoli next season to win the scudetto and as you said Simeone Inzaghi must be trusted again until next season. Apart from that, with a distance of 15 points, it has proven that Napoli will win the Scudetto this season and other teams in the top 4 have to fight harder to secure UCL tickets next season. Napoli are on paper with the first leg advantage and I think they will be very easy to get a place in the next round of UCL.
it is not certain that next season Inter Milan will be able to play better than this season or for Napoli it cannot be certain that they will perform well next season.
this season is still long I think we have to see how well inter milan will fight in the remaining matches this season.
for the time being, inter milan is the closest point to napoli. but 15 points is also a distance that is difficult for them to chase even if Napoli lose their form in 3 matches in a row.