You're right. In theory, Man City and Bayern Munich will be more difficult to beat Real Madrid. But it is not impossible that Man City and Bayern Munich can beat Real Madrid. Sometimes when a team feels that they are stronger, they become lazy to evaluate their weakness. So if Real Madrid is too focus on attacking, their defense can be so fragile and the opponents can beat them.
Manchester City will not be able to win Real Madrid next season because their players are not equal to the task, and if they cannot next season then they might not anytime soon. This is because if Pep leaves the club after next season no one's knows if the coach that will come to City will be able to strengthen the club the way Pep built it.
As for Bayern Munich, it is impossible for that to happen next season in the sense that they just changed their coach and brought Kompany who I don't think will be able to add much impact on the club's performance next season. He should focus more on how to win Bundesliga and not UCL because much is expected from in from the fans.