Not exactly. One or two defenders were always going to be part of Perez's transfer market.
No matter how strong the midfield and attack are, you simply can't win much if you have only Pepe, Ramos, Heinze, Marcelo, Metzelder and Salgado in defense. They don't even have two players for every position. An injury of one of Pepe/Ramos and all goes to hell. After Cannavaro left, they even have one starter less than last year, when their defense was again too shaky.
Maicon is perfect solution. You get the best full back in the world, you make the CD stronger by putting Pepe and Ramos there and the only weak link in the team remains the LB, but even here Marcelo might finally explode.
With Maicon it will be a well balanced team. Strong keeper, strong defense with full backs who attack and defend, one or two players to cover for the attacking midfielders (L. Diarra and maybe M. Diarra), Kaka, Ronaldo and the attackers responsible for scoring.
It will finally start to look like a hell of a team.