At the moment we're not playing with a holding midfielder or a creative midfielder so it's not surprise that he doesn't look like one. I'm sure both he and Dembele were playing how Sherwood wanted them too in getting involved all over the pitch, helping out in attacks, moving the ball forward and making sure we don't get overrun. Bentaleb has a pretty impressive passing range and I'm not sure you can judge what kind of midfielder he is just by recent performances, especially given the way our strikers behaved against Palace. We could've had Pirlo, Iniesta and Modric in midfield and we'd have still looked uncreative because there was so little movement upfront.
When I saw him in the U21s and Nextgen last season, he was playing the "grafting" role in CM. Putting himself about, bringing the ball to the final third etc. Thought he was a bit rash/headless in the tackle at times (which is why his performances in the seniors have been commendable) .
I've also been very impressed with Bentaleb and trying to figure out what kind of player he is. He strikes me as a kind of midfield manager, able to get the ball to the right people and himself to the right place. I agree that composure, or maturity, seems to be his strength. He's probably more similar to Dembele than anyone else on the team in terms of what he tries to do, and it's a bit odd to play them together, but I can see the sense of it. Two players like those two equals one creative plus one defensive midfielder.
Bentaleb looks like an all-rounder to me which is quite rare these days. Of course it's very early days but he reminds me a little of Dembele - good technique, can pass, can tackle/ intercept, gets forward, decent striking ability and can take on a player. At 19 he's looking like someone who's played in the league for a good couple of years, taking away the Arsenal performance, it's been a great start for him. Hope he progresses, will be an exciting player to have.