He's best as far from defence as possible hence the withdrawn striker role but in general with Bendtner, RVP, possibly Arshavin, and in the future Ramsey, Wilshire(Wenger has said he see's making Wilshire a Bergkamp in the future, the freaking moron, we need natural wingers, we finally get a class looking prospect and he wants to make him central, like every other player we own) and so on all who prefer that support striker role Diaby really doesn't have a chance.
I think what angers me most is, Diaby himself was on the recieving end of such a horrible tackle that was late, into ankle, too high and studs in and so he should be more aware than most how truly badly that kind of tackle can be. yet he does the same thing every single game without fail. I just can't understand the thinking, its simply better to not tackle at all, than give away freekicks constantly while trying.
One of the problems is Wenger seems to keep wanting to change how players play, bringing in people and changing their positions. Yes it worked with Henry, but now he is far to happy to push strikers onto the wings, Vela, Eduardo, Bendtner of late, when they are not particularly good there, or more to the point, much better in their real position. The problem is, every practice session Denilson has where he's trying to becoming a defensive midfielder, he loses something from his offensive game. 2 years ago he was showing almost as much creativity, forwards drive, passing awareness and passing ability as Fabregas and looked a worthy backup.
He's been forced into this DM position but while practicing defending, tackling and simply play, he's lost the other parts of his game completely.
Walcott's biggest threat at Southampton was getting inbehind the defence with his speed, yet at Arsenal we play him on the wing, he's not very good at getting past people despite his speed.
Buy a damn DM and play him as a DM, buy a winger and play him as a winger, buy a striker and play him as a striker. Versatility can be helpful for a few squad players, but not all your players.
Eh hes crap on the wing, the best i've seen him play is as a support striker. As you say his tackling is awful, to be honest he doesnt really fit in at Arsenal.
Seriously, the first game this year he played the support striker, was against Fenerbache, he was good in the first half, did nothing in the second, only goal this year, or maybe 1 of 2 in that game. he's played that role only a few times since then, and I don't remember having played him that far up the pitch ever before in his Arsenal career. before this year he'd started more games on the left wing than centrally in games which he'd been effective.
Think about it like this, what are his strengths. Quite pacey, can run pretty well with the ball and keeps it well under pressure , likes to get forward and has a good shot on him. Weakness's, can't tackle, not a fantastic passer, awful defensively in every way tackling, positioning, thinking, tracking back, marking and he's not really got the eye to pick out a throughball.
Those quality's equal a winger, its that simple. He's got no qualitys to be a decent central midfielder defence or offence. Hell he was mostly only good as the support striker for his shooting than his interplay, while pace and running with the ball is basically what you want in a winger. He doesn't "look" like a normal winger, that doesn't really mean anything though, Lennon looks like a winger yet is turd

He has the build of a Vieira but thats not remotely how he plays football. He showed the potential to be a good winger, but hasn't shown that for a while and hasn't improved a lick since he arrived to be honest.