A defensive midfielder often shifts to cover for an attacking fullback though. Raki was doing the role of a CDM far more obviously early on last season when he had to do all the covering for Alves and imo that was a large part of why we were so weak at the time. Putting in more defensive work to compensate for a non-defensive winger is him taking more effort defensively but I wouldn't say that's the role of a defensive midfielder. He puts in his shift on defense but that is not his primary role. Even you said he was poor, Bojan. His creativity has been poor and it's a stark contrast to when we have Roberto there, who not only helps defend but also carries the ball forward and can pick out the obvious forward pass.