Real Madrid's team this time is quite strong. Especially the defense has been strengthened by Alonso. Last season we saw Madrid's shaky defense. Real Madrid lost every match against Barcelona by a big margin. However, if Mabappe or Vini get injured, then Madrid will definitely face big problems. Hopefully that will not happen. Unless Real Madrid is very unlucky. Madrid has a strong squad. Alonso is also a very talented coach. I am waiting to see Madrid's success in the Alonso era. But so far we have seen that the Madrid squad is not completely stable. Even then, Madrid will start this season by getting 3 points against Osasuna.
Yes the Real Madrid board has seriously improved the squad most especially the defense by adding a center back, right back and also a left back. The defense has the brilliant Huijsen who I strongly think will be very important for the club going forward, then they have Arnold at the right back and most importantly the return of Dani Carvajal, both will be a good position there and also Alonso has the ability to twerk formation and accommodate both with a 3-5-2 or 3-4-3 formation where Carvajal can play right center back and Arnold plays Right wing back, same thing with the left side with the addition of Alvaro Fernandez also boosting the left flank with him been able to play either as a traditional left back or left wing back.
As for your claims about the attack missing either of the two players Mbappe or Vinicius when they are out injured I will say yes they will lack some quality but either of them out wouldn’t cause much of a problem as long as there is still Rodrigo who I think can fit in for both of them. The player though I think if he gets injured will be scary for Real Madrid is Dean Huijsen who we saw at the club World Cup as the bedrock of the team. Him been out means the center back pairing goes back to same thing as last season which is definitely a disaster