he's not a 6, but he's by far and away the best 6 we have, if he was on the picth, I don't think they get the second goal. Luiz's positioning on the whole is very good (which we take for granted, but is shown up when he's off the picth and Mcginn, Ramsey or Sanson try to take over).
But agree we need a big strong dominant midfielder, and Luiz next to them, let him fight it out with Sanson, McGinn, Ramsey for the 2 8 places (maybe chuck too).
For me it's the most importnat position on the pitch, and like others I want a commanding presence there, but I would love us to keep Luiz as an 8 or as a 6 alongside another 6. I think his ceiling is really high.