Real Madrid's performance will not decline next season either; they will gain more strength because of the presence of Mbappe, although even before Mbappe came in, they were doing very well. Furthermore, I think the Champions League will be very tough this season. Arsenal, Manchester City, and other teams will want to take down Real Madrid, which won’t be a difficult thing for them. But it will be too early to predict how teams will perform next season, so let’s watch and see.
The presence of mbappe isn't the sole reason Madrid is going to excel in strength next season, but it will add to it because he's a good quality player, before now Madrid has got good quality, such that they will be able to even maintain their well enough even in the new season, I believe that Madrid is a team that isn't dependent on a player so their strength too cannot not be quantified on the basis of a particular player, there are other top players who will add to the strength of Madrid and it's going to be a total collective effort from all sides joined together.
Putting Arsenal as one of the reasons the champions league will be tough this season is not totally out of place but then I see some relativity around it because I still believe that Arsenal will be able to make an attempt to go beyond the knock out stage but then champions league has not been something they have really be able to handle well enough in the past years they have been playing in the champions league, at this point it even looks like the premier league is of priority to Arsenal but Manchester city and Madrid are going to be big teams in the champions league most definitely.