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.
Real Madrid have won the UEFA Champions League title for the 15th time and they're the best club in Europe after surpassing every other club when it comes to major title won. Real Madrid will continue to dominate because they've everything within their reach. While Manchester City and Bayern Munich are formidable for the UEFA Champions League next season but they're not the only ones that will take it to the next level, we have Real Madrid and other elite clubs that will fight for the very best.