We have a pretty decent 2nd squad to be honest. Just get rid of Chamakh... but hold onto Arshavin. The talent is still there. A major reason why we struggled last season was because of depth. Unless we have an oil sugar daddy, our bench is never going to be filled with world class players, but it's decent enough to challenge for the title.
Did you see him bomb forward aimlessly? I didn't. That shows restraint on his part, ergo, discipline.
He's nowhere near Song either defensively or otherwise. Song helps out offensively but he has a huge presence defensively as well. Starting Coquelin ahead of Song unless he's crippled/injured is about the worst team selection mistake one could make in our squad IMO. (Heck, even Fabiansky ahead of Szczesny would be less dangerous)
The only prescence song has defensively is the giant gaping hole he leaves for the opposition's CAM to roam free in, after he's wandered off upfield. Coq actually fills me with more confidence. Song can go to barca, we can get someone like Capoue instead, at least he knows his role.
From other posts, I gather that you are quite old and also a fan of this club for quite some time. Please look back on previous seasons where Song was used as a cover CB (very competently) in the past for Arsenal. He also played an ACON almost exclusively as a defender a while back, doing very well. Wenger was very clear in multiple occasions that Song is playing the way he intends him to play. If Wenger would ask him to play the classic DM role, he would. But the utility he provides is obviously welcome, so he doesn't.
It's no one's fault. It's just a choice. And like with any other choice, there's always tradeoffs. You could say we might have conceded less last season if Song was focusing solely on defense, but how many goals less would we score (not just Song assists, but initiations also) and how would our ball possession be affected?
Gent is right. In 2009 Song played in the 'holding role' (it was his best Season for us) Since moving to a 4-2-3-1 Song has been given more licence to get forward. The idea being that Arteta sits while Song goes forward and visa versa.