Spalletti also had some problems. If you remember the season before they won the title, they had a great first half and then completely failed in the last third of the season. In the championship season they also played significantly worse at the end of the season but by that time everything was already decided. Conte is in his first season at Napoli and I think he is doing great, in the following seasons Napoli will continue to progress and perhaps win gold.
I remember at that time Spalletti seemed to give great hope but after that he didn't give any results except worse results than before. 
But for Antonio Conte, at this time I still see good hope, it doesn't seem to give great hope, but in terms of managing players, Conte looks neater. Losing Osimhen and Kvaratskheli is not his fault but sometimes the intervention of the management. I prefer to see the team develop slowly and be able to get improvements every season. Hopefully Conte can do all of this.
Yes, Spalletti failed with the Italian national team after leaving Napoli, he was one step away from not making it to the World Cup (Italian fans would probably go crazy from missing out on another World Cup) and there was also a failure at the European Championship. It seems that Napoli was his peak. As for Conte, in my opinion, he shows results higher than expected and if he progresses, Napoli will have a chance for another title.