It's not always easy to defend a trophy, all contestants will try to perform better next season. PSG made history by winning their first Champions League, as we know at first they were not the main favorites. For next season, maybe everyone will be surprised again with the emergence of a new champion. But in theory, Madrid, Bayern Munchen, Inter Milan, Man City, PSG, Barcelona are some teams that I think will compete tightly for the trophy.
On the other hand, the change in the Champions League format, I think has given a greater advantage to teams like PSG and Bayern Munchen. I mean, both teams are very dominant in their respective Leagues, where they are easier to compete without getting much pressure, so they can divert their attention more to the Champions League. However, we will see what will happen to both teams next season.
It depends what trophy we are talking about. National trophies, if there is one team that is far superior than the rest, are easier to defend then of course. But the Champions League has always been one of those competitions that no team was able to defend ever, until Real Madrid finally made it happen.
All those teams like Manchester City, Bayern, Barcelona, many others have tried over and over again, but the bottom line is that Real Madrid so far was the only team able to defend it three times in a row.
It is going to be another exciting season with that new mode I think and I believe the UEFA is planning some more improvements, but defending the title will be as hard as ever.