Strong clubs in the Champions League on average have a strong economy that supports teams to bring in quality players, it is easier for coaches to bring in the players they want because of strong economic support. Manchester City have proven that their economic power is able to improve the quality of the team by bringing in classy players. Guardiola's effect was also very influential in Manchester City's success last season, he who has experience winning the UCL trophy with Barcelona was able to develop the players that Manchester City has to achieve historic success for the club. This season there will be more tough opponents in the UCL, Manchester City will have difficulty defending the UCL trophy if they are not consistent in maintaining the quality of their games.
Although some of the teams participating in the Champions League are not teams with good financial status like Barcelona, I believe their performance can be expected. Manchester City will certainly have a lot of trouble defending the Champions League title, but that doesn't mean they can't win it for two seasons in a row.
All teams will fight to get a ticket to the final, but there is no guarantee for anyone even though they have been the favorites from now on. I admit that Manchester City are the favourites, but Real Madrid will not lose to the favorites next season either. Arsenal, Inter and Napoli seem to be the same, but PSG cannot be underestimated with Bayern Munich either.