Real Madrid have dominated Europe without kylian mbappé, so even if he comes into Madrid, it's to just help and improve on the already existing structure Madrid have, even in the absence of Ronaldo and benzema they've been outstanding in their performance, currently they are in top gear both in the champions League and their domestic league, sitting at the top of the table with 72 points, and are likely will be the title winners. I know the game between them and Manchester city is always a tough one, but with the current statistics, they are in a better position to win Manchester city.
I do agree that if he joins then they are going to keep on dominating. We are still yet to see what will happen with City, because last year they lost but to be fair we have seen City to win it all, they were treble winners and that's important.
But, we need to remember that we are going to end up with maybe City winning or maybe Madrid will win. What matters however is that Real could be a lot better with Mbappe on the squad next season, nothing is guaranteed at the moment but we can see that they are going to be pretty good and we are going to see them do pretty well. This is why I think this move will change the power dynamics of the whole world and put Real at the top for a long time, they will dominate the whole world.