Arsenal's midfield has been very imbalanced, partly because of Jack Wilshere
Ever since Abou Diaby limped off 3 and a half months ago, on the 28th of September, Arsenal's midfield has lacked the balance between their defensive responsibilities and their offensive duties. The dynamic that worked so well in tough away games against Liverpool and Manchester City has been, in most games, missing, giving Arsenal's midfield a slightly chaotic look. The return of Jack Wilshere has added more creativity and dynamism to a midfield that had been lacking those traits, but Wilshere's inclusion has also come at a cost, creating imbalance in the middle, overloading Mikel Arteta, and creating too much space between the lines for opposing teams to exploit, thus leading to more chances for opposing teams to play through Arsenal and score.
The imbalance occurs from two problems: Arsenal's pressing this season has been inconsistent in duration and shape, and Wilshere sometimes tries to fix problem by charging around the midfield. While such devotion to the cause is admirable and endearing to the fanbase, Wilshere's one-man pressing band leaves space behind because on most occasions, the rest of the team, either because they're adhering to Arsene Wenger's instructions or because they're psychologically fearful of pressing, fails to press with him. Thus, simple movement and passing puts an opposing player into space, and gives Mikel Arteta more space to cover. That's a problem for Arteta; he works in a double pivot, but not as the sole holder because he lacks the physicality to cover as much ground as a player such as Alex Song could.
When talking about his role as the second midfield in Arsenal's double pivot, Abou Diaby seems to have a better understanding of the necessities of the role, saying
I have defensive duties as well so I need to have a good shape defensively and, as soon as we get the ball, go forward
This is borne out in the statistics; Diaby has more tackles and interceptions than Jack Wilshere, and has fouled fewer times and been dribbled past a fewer amount, showing that Diaby's defensive positioning is better. Thus, the lack of Diaby is one reason why Arsenal have become more open in recent weeks. Offensively, Wilshere does offer a bit more, and is a better and more creative passer of the ball, which is why even if Abou Diaby were to become magically fit or Arsenal buy alternative, the answer to this midfield conundrum is not simple. Wilshere's creativity, although not his final ball, is a major reason why Arsenal have become more dangerous going forward, and taking him out of the team would take away some of that creativity.
There is, however, one possible solution if Arsenal were to buy a defensive midfielder or Diaby were to be horse placenta'd. When coming though the Arsenal academy, Jack Wilshere played as a #10 and also as a right-winger, a role he played in when Arsenal's Young Guns impressively beat Sheffield United 6-0 and Wigan 3-0 in the 2008/09 Carling Cup. It'd be a role not entirely dissimiliar to what Yossi Benayoun did on Arsenal's left last season; an extra, creative player that can help retain possession and help Arsenal control the midfield, which they've been unable to do against Southampton, Newcastle and Wigan. If he were to play on the right, he could naturally come inside and play quick one-twos to get out of pressure, or to play longer-range passes. Yet, on the right hand side he'll also have to play higher up the pitch and combine with Arsenal's forwards. This can help him with his final pass, and help him transition into a number 10. Right now, the quality of Wilshere's final pass isn't there yet; too often, it'll be over hit, or he'll pass sideways than playing a through ball through the middle. Until he's able to do that, Wilshere won't be able to play behind the striker without affecting Arsenal's creativity, but, if he were to play on the right, he could help Arsenal keep possession and create chances with link up play, while working on his final ball.
That would enable Arsenal to defend better across the pitch. Wilshere's pressing wouldn't open up as much space, and he'd be more likely to track his full back than someone like Theo Walcott or Gervinho. Furthermore, Arsenal could play a more solid defensive player with Mikel Arteta, which would better help Arsenal replace Alex Song. It's often forgotten that when Mikel Arteta played last season, Arsenal were a fairly solid defensive team, conceding only 28 goals in the 29 games he played with Alex Song. That midfield had a good balance; Alex Song could create from deep or push further forward, with Arteta covering, or Song would sit and let Arteta go forward. This season, when Diaby played with Arteta, Arteta was far less likely to go forward, giving Arsenal more defensive cover on counter attacks, but, crucially, Diaby would come back and form a good shape, something which Wilshere has been unable to do thus far.
Perhaps Wilshere is feeling the increased pressure to do something, especially with Cesc Fabregas no longer playing in the midfield. Thus far, though, he seems unable to fully understand the role he should be doing to best help Mikel Arteta and best help Arsenal's defence. With his final ball not as good as Santi Cazorla's or Tomas Rosicky's, he shouldn't be the #10 either, leaving, if Arsenal want to be better off the ball, only one solution: out wide. There, he can improve his final ball and better link up with Arsenal's forward players, while giving the midfield more control than it's had in recent weeks.
If Arsenal are to regain a good level of consistent form, all of that will be important. Moving Wilshere can not only benefit Arsenal, but it also benefit his own development as a player, both of which are better for Arsenal in the long run.