Actually in terms of tactics, I think this is not too big a difference when Spalletti and Rudi Garcia especially if you look at the formations and schemes carried out, Rudi Garcia actually only tried to adapt Spalletti's strategy last season, it's just that in this case there is a difference where the execution of the strategy carried out due to the shortcomings of Garcia himself.
Tactic is only one component and there are many things in a club. Napoli won Scudetto in the last season when they were an underdog but do you think they are still an underdog in this season?
They are not and clubs in Serie A no longer consider Napoli like this. Even if Spaletti is still in their club, Kim Min Jae did not move to Bayern Munich, Napoli will have bigger difficulties in this season. It's hard for them and any champion to defend their trophy.
It is difficult to equalize performance when coaches are different because even though the players and schemes are the same, the execution is clearly different and this makes the results different.
Rudi Garcia has a bigger task than Spaletti and he is carrying more pressure than Spaletti too. He is a good coach but left Europe a few seasons to work in Saudi Arabia and with this return to Europe, participate in Serie A, he is facing with a big mission. First he must adopt to Serie A a second time and second he must help Napoli to win Scudetto again. In history, Napoli has never won two Scudetto titles in two consecutive seasons. So requiring them to achieve it in this season is somewhat too much.