Real Madrid won last season, they performed very well last season so no one thinks that their performance will decline, regardless of whether Mbappe is there or not, but basically Real Madrid is a strong team, but it must also be admitted that Mbappe's presence will help make the team performance better.
Mbappe is indeed a player who has very good qualities and in fact he is one of the best players in the world today, but all players who join a new team of course need time to adapt, and so does Mbappe.
I think there is a very big possibility of dominating La Liga next season because their rivals Barcelona are currently in a slump with all the problems they have.
Barcelona spent the end of the season very well, so now it’s not worth saying that they are in decline, especially since they have a new coach and this often gives the team a good boost. I don’t think that Mbappe is capable of somehow improving Real’s attack, especially in the form he is in now. He will have to work well with Ancelotti to improve his condition, only after that it will be possible to talk about whether he can give something to Real Madrid or not.
I agree with you that Barcelona is in a good form compare to the way people are looking at it. I think the reason why most people feel that Barcelona might not be able to improve their performance is because Xavi that managed the club at this current financial state is longer there again to continue from where he stopped. Assuming he is still the coach we might want to see how he would have being able to challenge Real Madrid with Mabppe in their team, you should also know that it was difficult for Barcelona to win Real Madrid last season. With the change of coach nobody knows what will be the fate of Barcelona because they are broke assuming they would have pump funds into the market to also equipped their team to the standard of Real Madrid. Mbappe will do better in Real Madrid because he has all the players to make scoring easier for him.