It's relevant enough so here are some scattered thoughts on the midfield.
I think we generally look most competent with a midfield three, provided we have the right mix. In particular, we need:
1. someone who defends - Gana, Schneiderlin, McCarthy, Bangingime
2. someone who plays box-to-box - Davies, Klaassen (?)
3. someone capable of applying the final pass/finish - Sigurdsson, Rooney, Klaassen (?)
You can see the problem from a squad construction point-of-view. We have too many one-note defensive types and not enough players capable of affecting games going forward.
I'm not sure where Klaassen falls between 2 and 3. Ajax supporters seemed adamant that he was a box-to-box player but he hasn't influenced games much when he's played in that role. All of his best contributions have been deft touches or clever bits of movement around the penalty area to create chances for teammates/himself, which suggests to me that he's more of a "finisher."
I think where we've generally gone wrong over the past season-and-a-half is that we play too many players from category 1, which causes problems getting the ball into the final third, creating/scoring chances, and, strangely enough, defending (when we play 2 DMs, neither stays put, often leaving too much space in front of the defense). Koeman ran into this issue with the Schneiderlin/Gana combo after AFCON last season and at the beginning of this season. Allardyce is running into it again now, for some reason (he started with the balanced Gana-Davies-Rooney trio and hasn't gone back to it). Take Saturday, for instance. One of the reasons we were so ineffective in attack is that West Brom regularly forced us to check back to McCarthy when we built down the right and McCarthy isn't any good in the final third (they did the same thing with Cuco on the left but, unfortunately, we don't have another option at LB right now unless you're a Garbutt fan).
Allardyce would do well to stick with only one defensive type from now on. Any decent football we've played has come from that type of configuration. It's the only way we get any sort of control of the ball. Two DMs in a midfield three means lots of hoofs with no one to feed off the scraps.
If he absolutely has to play two DMs and go full-on anti-football, he should consider changing the shape to a 4-4-2, with another central player further forward to feed off of knockdowns from Tosun. Walcott, or maybe even Klaassen, might fit that role (Niasse needs to be kept on the bench; he's a fantastic sub).