IMO, actually Al Nassr's defense line is filled by Alex Telles and Aymeric Laporte, these two players have experience and abilities above the average of local players owned by Al Nassr's defense. two local defenders who are often the main starters, they also performed quite well. the focus is not only on the defense, but overall. so is the goalkeeper, they have Bento now. the role of the midfielder should also be a concern and as we know, if Luis Castro often uses two pivots. if these two pivots do not help the defense much, it is clear that it will weaken the dangerous area in Al Nassr's defense. for me Al Nassr is a very competitive team, but it seems that the problem is not only in their defense. I think Luis Castro is the one who has to evaluate his system and strategy. especially, when Al Nassr plays against fairly strong teams and their rivals Al Hilal. well, now Al Nassr has brought in a young winger from Brazil. I'm not sure if this is a good recruitment, considering he is still young, but Al Nassr's squad should be more competitive. Well, let's see how Al Nassr progresses throughout this season.
When we talk about a defense line, the goalkeeper and the defensive midfielders are included the same the same thing applies to when we talk about attacking line wherever the attacking midfielders, wingers and strikers are included. Al Nassr's problem in the last two seasons is nothing more than their poor performance of their defense line and that has cost them a lot during these times. From your analysis, it obvious the club manager already have taken notice of the weakness of his team and would therefore work on it with the best available players at his disposal. Personally I would want to see Al Nassr challenging for the biggest trophies this season.