He doesn't have dynamism to fit in a box to box role that we need. He is a pretty defensive midfielder. I would be happier with Cleverley playing next to Carrick than Gustavo.
That he is and I don´t see the problem with it. Gustavo would walk right into the starting formation and improve the squad a great deal. You bring up dynamic and creativity, but the thing is, that he would bring exactly that, just not personally.
What he would do, is bring something to the team that is sorely missing right now: much needed defensive cover for Carrick. The latter is right now very often forced to play more defensively than ideal. Carrick could potentially contribute way more to the offensive, if he had the chance to do it and would not be forced to cover so much area, because of a shaky partner.
Gustavo would bring them stability, consistence and very good pace control. He has several strenghts: impressive passing range and accuracy, good tackling ability, excellent positioning and a good shot, but he is far from being a stand out players. He contributes a lot to the game, though. More often than not that becomes clear, when he was missing.
Defensive midfielder often stand in the shadows of their creative counterparts, because they don´t make the big plays. What is often forgotten and rarely mentioned is that workers like Khedira, Busquets, S. Bender or said Gustavo are the main reason, why the CM are able to play the way they do. They can take more risks and go for the bigger plays, because they know, that they have someone watching their backs, who can clear up the mess they potentially create.