Currently it is only Manchester City and Real Madrid that is the strongest in UCL, and it is only Manchester city that is Real Madrid rival. Any club that is in its best form has the chance of winning UCL that season. This was what happened when Chelsea won UCL. However, luck is also part of succuss because if you are not lucky, you will not be able to overcome tough clubs like Real Madrid.
Next season will favor Real Madrid more only if City can stop them but I doubt this can happen because scoring goals would not be a problem for Real Madrid anymore now that they got Mbappe as their number 9 striker, he will be scoring very easy because he will have all the assist he needs.
You have already stated the fact, as is known to everyone, that Real Madrid and Manchester City are the two strongest teams as far as the Champions League is concerned. We might still think that this will still happen in this upcoming season, but to be sincere, Real Madrid are going to be super strong as far as this upcoming season will start because Real Madrid with mbappe is a new definition. So I know that Real Madrid will display a new performance that we will never expect, but it is also luck, as you mentioned. So even with the talented players that will be present at Real Madrid, they might still not get the victory of next season.