The midfield is the heart of a team, so when the midfield cannot have a good balance, then the risk is that they are easily shaken. I agree that besides the defense, their midfield must also be fixed to provide a sense of comfort and balance in the game. The midfield is very influential, because they must be creative in attacking and must be strong in defending, so before the opponent can enter the defense area, they must stop it in the midfield. Al Nassr still has problems there, or they have not been able to consistently provide a good game in every match they play, so this must also be considered by the coach.
Also Goalkeeper, I know they have Bento, but dude is just not good enough at all, not even nearly. They need to get an actually great player, even if that player is old, they need success now when they have Ronaldo, so ignore the age and get the best you can get. Look at Ederson and Alison, both are looking like they could be bought, specially City looks like they are willing to let him go, that could actually be amazing for them, certainly would be much better than Bento if you ask me.
Ederson may have some adjusting period, plus he hasn't played all games, Ortega did and that is why I believe that Ederson may sometime adjusting, but they should really consider if they could get him and make him play, it could be awesome for them. Obviously they could also get other players too, like KDB said he is willing to play at Saudi League, so maybe doing a package deal with both of them could solve all of their issues and they could end up with a great future.