In fact, there is nothing impossible in every match or if the match before 90 minutes is called, the match could possibly have a team that is superior or not, it all depends on who luck favors, Barcelona could win Laliga next season, although Real Madrid having just brought in Mbappe does not guarantee that a star-studded club will always dominate the league or game, in fact a non-top club could conquer the king of the league.
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.