you cannot compare the state of the league and the teams benitez and allegri inherited
allegri is backed by the best management in football, benitez was given an inter side who had the last bit of them squeezed out by mourinho with no improvements...+ that milan side that won the scudetto with allegri is much better than any side that has "competed" in the past 6 seasons.
napoli are a good team and tbh if they didn't have a weak dork as a coach, would probably be able to win it.
sarri's teams will always crumble, no matter the club he's at. he's weak and always looks for excuses, and that reflects on his team.
and before some clueless sarri fanboy comes out with the money excuse.....wolfsburg, atletico madrid, monaco, montpelier, dortmund x2 and even leicester all did it