The Il-2 is fantastic against every vehicle except the Ostie. The problem is, almost every vehicle is an Ostie. Against the Ostie it is not really any better. What it makes up for with big cannons and the possibility of surviving a hit, it gives up in horrible climb/speed, and the small size of bombs. Seriously, the P-47 with a good dive is a better anti Ostie platform because it's speed is more effective than the armour, and the 1K bombs it can carry give a large enough blast radius to knock out an Ostie. The Il-2 simply has to get too close and is too slow to really get into the target unscathed. You can dive-bomb, but the awful climb rate simply doesn't compare.
It's not really a problem with the Il-2 in my opinion, it seems fine against almost everything, but it's a problem that the Ostwind is overpowerful and numerically dominant.
-Soda
The Assassins.