Not sure if this also applies to Serie A, but in some leagues, the winner is decided based on their second-half performance of the season. I remember that Man City usually stumbles in their first few games over the last few years (including when they won so many trophies). I think the competition was even tighter last season, right up until the last few games for Serie A, too? So yeah, I'd also think twice before making a bold prediction on who will win the league this early in the season.
I would tell you that it very important to start the league with a high spirit, which is winning your matches. No manager or coach want to start their league run in a bad way. And again you said Manchester city usually stumbles in their first half of the season, I would say you are wrong, base on statistics Pep has had the high rate of winning in the first half of the season aside last season. When you contend for the league, winning matches in teg first half of the season is super important, and it not just Seria A it applies to all leagues.