Pirlo unaccountable? He's the best defensive midfielder in the world by an absolute mile.
Mascherano = yes way.
Also, Claude Makelele, Gennaro Gattuso are also both better defensive midfielders.
Pirlo plays more of a Cesc role - playmaker, not a defensive midfielder/enforcer-esque player as such, which is what Flamini is. The two cannot be compared.
Flamini has been the best defensive mid in the league this season. Better passer, marker (marked Kaka out of two UCL games) and runs more in a game, amongst other things in comparison to Mascherano. Makelele, on this season's form, doesn't come close i'm afraid.
Gattuso is completely past it and similar to Makelele in that this season's form hasn't been flash. 1-2 years ago he was the best, however that's not the case anymore. Flamini is widely regarded to be better.
What about the 5 others you were speaking of?