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.
It is quite surprising that Bayern Munich has a chance to beat Real Madrid because after all, to get the Bundesliga trophy next season will also be very doubtful. Because anyway, it looks like Bayen Munich appointed the wrong coach and thus, it looks like to getting good results in the Bundesliga is also likely to be difficult for Bayern Munich next season. So, there is no chance for Bayern Munich to make it to the Champions League final.
But about Manchester City, if for example Pep Guardiola declares to leave at the end of next season, then of course Pep Guardiola will make the best and maximum effort to give Manchester City good results before his departure. After all, basically Manchester City in the Pep Guardiola era is still a great team, and of course always has the chance to go further in the Champion League. Therefore, it is not surprising and not something wrong if Manchester City may always be said to be a difficult opponent for Real Madrid.