I dunno about that, flamini on the side allows him more movement forward, which he is very good at. Think back to siena game, his run to assist (pass from dinho)... i cant see any of our other mids (minus abate) making that run.
The reason Flamini is starting ahead of Ambrosini is because he is quicker and more mobile. Flamini is the midfielder tasked with doing everything - that is he is meant to get up and support the attack (as you highlighted), and get back and defend. Again, you correctly point out that he is the only midfielder who does this attacking role.
However, he is there because he can get back quickly to support Jankulovski. He can supposedly do both roles effectively. Problem is - he can't. Every one of the goals we have conceded this season have been from problems on the left. Flamini can't keep supporting the attack, and then getting back and helping Jankulovski because no player has everlasting fitness over 90mins. He will naturally get tired. Look at Thiago Motta's goal, he just cantered past both of these two. Why? My theory is because of the short term fatigue that comes with having to sprint back.
This wouldn't be a problem if we had a proper DM instead of Pirlo. 3-5 years ago, Pirlo would be fine to cover because he was younger, fitter, and quicker. There was an incident in the first half where he tracked Zanetti to our goal line and tackled for the corner. He used to do that a lot 3-5 years ago, meaning his position in front of the defence was sustainable from a defensive point of view. He doesn't do that anymore - that incident was the only time he did in the match - and so his position there is no longer sustainable.
Therefore, we have to adapt. We can't expect our players to perform the same roles they did when they were 5 years younger. Now we need a proper DM in front of the defence. That way, we have a proper defensively minded individual who can cover and make tackles (along with Gattuso, who does this well anyway). Jankulovski knows there is greater security behind him, and Pirlo can use his talents further up the pitch.
Look at last season. Pirlo was out from September-December. He missed 14 games. What did Ancelotti do? With no Pirlo replacement in the squad, he used Flamini (and sometimes Gattuso) in front of the defence. What happened? We didn't lose any of those 14 games. And we won 12. Those results speak for themselves as far as I am concerned.
Exactly. Very True. Flamini would do a great job in Pirlo's place, but we would miss his speed on the wings.
Flamini doesn't really play on the wing. He is more to the left, but the proper width is provided by the full-backs. In any case, yes we would miss his pace. But we gain Pirlo, who has far more attacking talent, further up the field.