I think people are underestimating Denis a bit here.
1. He hasn't gotten a fair chance to show how he would perform in a midfield that was working properly. He's surrounded by a mess. Not gonna blame him for not creating when he's got no space.
2. Under the circumstances he's been playing, I don't think he's done bad lately. Not that this in itself is any particularly impressive accomplishment in context of his two counterparts, but he was our best looking CM against Malaga and Sociedad. Actually looked like he wanted to take charge and chance the game with the ball by his feet. Also impressed me at Sanchez Pizjuan.
Not a world class player, but miles closer to being the real deal than Rafinha.