Having a star join them doesn’t actually guarantee they will be successful again next season and dominate the league but it actually increases their chances of dominance over other teams. Just imagine what Madrid have done this season without a serious striker and what they will be capable of doing if Mbappe adds his expertise and goals to the club, i think they would be unstoppable next season.
Had it been they changed coach they i would agree with you but since Ancellotti will still be in charge i believe nothing will change. Barcelona cannot be written off though but the fact that they changed coach can be difficult for them to have a good season, it might take the coach sometime to settle in the team and find his balance.
All possibilities are still possible and although Barcelona cannot be underestimated, we also have to look realistically at Real Madrid which has been built with a fairly strong squad in all areas and most of them are young players so that in the next few seasons the Real Madrid team will have quite balanced strength.
Barcelona's decision was very correct, they made a lot of effort even though they were having a lot of problems and replacing a more experienced coach had good possibilities even though it still looked difficult.
As for Real Madrid, we cannot deny that recruiting star players who have good quality will have a big impact on the team if it is supported by equal distribution of the squad in all lines, that cannot be denied.