I don't really get the comparison - Carrick has a lot more to his game than just cleaning up. My worry with a player like Matic is that last season our attacking was very limited: we have very little attacking threat coming from full back and our wingers have been poor. Arguably we may be worse off now, since, though Lukaku is a good goalscorer, he strikes me as less creative than Ibrahimovic. If we start regularly deploying a destroyer in midfield we risk becoming even less creative. I understand that the argument is that it could free Pogba from all defensive duties, but It'd much rather see us sign someone more like Carrick and less like Matic; someone who can sit relatively deep but who is a a bit more incisive in his passing.
I wasn't comparing the two, and I know Carrick has a lot more to his game than just cleaning up, but that is one of his many attributes, although I personally feel the need for a deep lying midfielder is becoming a bit overstated, in my opinion.
For example, Spurs created the most chances in the league last season, and they play with at least one, if not, two out and out defensive midfielders in Wanyama and Dier.
If a 4231 is played correctly, the creativeness should come from the front four and attacking full backs. Yes, a defensive midfielder can get involved in the attacking play from time to time, if/when needed.
That said, creativity wasn't our problem last season, it was actually finishing off our chances. We created more chances
(447) than champions Chelsea
(446). Our problem; however, was finishing off our chances. Lukaku, along with a goalscoring winger and a number 10, who will get us 10-15 league goals should solve this problem.