#3 Lack of a proper system

So the lack of a proper defensive system has been an issue in Real Madrid ever since 2017-18. Without a proper defensive system in place, Real have been conceding goals left, right and center.
The only reason Real Madrid won the Champions League that season was that the offense was still functioning and the team had Cristiano Ronaldo, who could bang in goals when needed.
Without the goal-scoring machine on their side, Madrid has often struggled to score goals as evidenced by their record-breaking goal drought last season.
Real Madrid with Ronaldo, in his last 2 seasons, scored 2.79 and 2.47 goals per game respectively. Without him, in 2018-19, this dropped to 1.66 goals per game.
This lack of goal scoring prowess would still have been okay if they had a proper defensive system in place. Real Madrid conceded 1.21 goals per game in 2018/19. Compare this to FC Barcelona and Atletico Madrid who conceded 0.95 and 0.76 goals per game respectively, it shows how much the Whites concede as compared to their direct rivals.
Real have world-class defenders on their side but still concede some thoroughly avoidable goals. They don't have players who can score tons of goals, and the lack of a proper defensive structure leads them to concede goals.
Of course, this was just a pre-season friendly and it is better to lose in such a way now than to lose during the season.
Zidane still has time to fix all these issues before the season starts and there's still hope for all the Madridistas around the world.