They have good lines, front and back lines even in the middle too. They have had good long term strategies and preparations for departure, retirements of Kroos, Casemiro, Modric, Ronaldo, Bale with many young players bought recent years like Vinicius Junior, Rodrygo, Valverde, Tchouameni, Camavinga. In defense system, they need to be more quickly with prepare for next 3 to 4 years to replace Alaba, Rudiger and Militao. With good preparations for defense system, they will have very balancing and strong team in coming years.
Regarding the defensive system at the back, I think Real Madrid have also started to think about this with the aim of replacing Alaba, Rudiger and Militao when the time comes. I believe in Real Madrid's movement in recruiting players for every line they need, because apart from being able to rely on money they can also rely on clearer vision in bringing in players into their squad every season. And next season it looks like Real Madrid will become kings of Europe again by winning more trophies because the potential of their players is very good.