I think assuming the best just because we reached 100 points last season and think that is going to happen again is so stupid. We wont the league with Mancini and the season after we were shit and werent even in the title race really. Same after Pellegrini's title where we scored above 100 goals and scored 5 vs Arsenal and 6 vs Tottenham etc.
Mentality has to be perfect for a start when you start defending your title. Teams are going to try to put extra shift in vs Champions. Players cannot feel like they have made it now and success wont have to earned by working 110% hard. Pep could be a guarantee to thats not happening but still some players might be happy with what was achieved already.
Having new players coming to the team making it stronger is a must. We want to do well finally in the CL too and we are coming up short the Monaco/Pool ties showed it even wih Guardiola. If we cannot beat these then Bayern, Barca, Real on their day wont give us a chance either.
Juventus won their league yet they went for CR too.
Barca won their league yet they have big plans for this summer, missed out on Griezmann earlier...
Not even mentioning even things can click for our rivals too and they might get just 10-15 points more than last season while we get 10-15 less. That would make it pretty close title race.