Considering Real Madrid isn't your average team, they'll be playing a lot of matches next year as they aim to win the Champions League and La Liga titles. Barring any major surprises, they'll likely reach the Champions League finals. This means a high tempo of matches. Therefore, playing matches without rest is a major problem for Real Madrid's players. Therefore, I believe the Spanish Football Federation should have postponed Real Madrid's first match.
You are being a bit too optimistic about Real's chances for the new season. With the way they played against PSG, they might not even reach the final. Because with that kind of defense, you cannot expect good results. Although on the other hand, their main defenders might still find their form and everything could change. But for now, I do not see any big improvements in Real's defense. Of course, they will always set the highest goals for themselves to reach the Champions League final and even win it, but for that they need to strengthen their defense. And actually, PSG did not manage to score a single goal despite such a strong attack, so that is also something to pay attention to.