I wouldn't say he was a midfielder in that sense, no. When Silva said he was competition for Sigurdsson I would assume he meant in the position Sigurdsson actually plays for us, behind the striker, rather than competition for if we ever decided we wanted to play him in central midfield.
We do struggle to break teams down but just filling the team with more attacking players doesn't necessarily solve that. It often makes it worse. One of the main reasons we have managed to break teams down eventually is Gana. His ability to win the ball back every time teams try to break, and to press high up the pitch, has allowed us to put on relentless pressure until teams crack. Losing that means you become much easier to play against, and means players like Gomes and Sigurdsson end up wasting themselves doing defensive work instead of being able to concentrate on what they're good at. Football isn't just about getting 11 skilful players on the pitch, the team has to work as a whole. It's one of the reasons why I think Walcott - or someone like him - has to be in the side. If Lookman plays it should be instead of Bernard not Walcott (he shouldn't by the way, I just mean he's more that type of player).