Your idea would be a big fail, for two reasons : - If Luiz can make those great runs forward, it is because he is playing in the defense. Thus, he has a lot of space to start to run, and has time before someone comes to close him down. If he was played a bit futher high on the pitch, he wouldn't be able to make these runs, because he wouldn't have the space he is granted while playing at CB, and he would have someone closing him down permanently. - If he plays as a defensive midfielder and keeps doing those runs, it would be catastrophic for the team. Because he would give to much space and freedom to the opponents, and would leave our two CBs alone. And, an defensive midfielder isn't supposed to make runs forward.