Sarri did a great job at Napoli. While it's true they were already a good side, and he didn't radically alter the squad, he also made every player better (particularly Mertens) and improved the side even after losing their best player, Higuain. Napoli easily played the best football in Italy last year, they just had a very small squad so were bound to find it hard to compete for Seria A and in the later stages of the CL, so Sarri deserves further credit for pushing Juve all the way in the league.
Sarri did a great job at Napoli. While it's true they were already a good side, and he didn't radically alter the squad, he also made every player better (particularly Mertens) and improved the side even after losing their best player, Higuain. Napoli easily played the best football in Italy last year, they just had a very small squad so were bound to find it hard to compete for Seria A and in the later stages of the CL, so Sarri deserves further credit for pushing Juve all the way in the league.