Well, I'm not going to say that it's easy to beat an armoured company with a normal balanced list (it's not!), but it's only totally impossible if you stick to just playing "line up and kill them all" games. If you actually play missions from the rulebook those tanks
have to move if they want to win, and moving greatly decreases their resilience. If they move up they are exposing their side armour, as well as reducing their firepower. Add to that the fact that normal troops can take advantage of cover and the fact that their own models will always block LOS to their other models and you've got a recipe for a somewhat fairer game.
I suppose the only exception to this would be seek and destroy, but even then you'll have the advantage because you'll probably have more scoring units, so you can just hide them and gain points for them.
I don't know about IG, but my normal eldar list can handle an armoured company without too many problems. Then again, my normal eldar list has three vibrocannons, Eldrad and his eldritch storms, and a
bunch of EMLs, so perhaps it's not quite fair.
Besides, the baneblades are a red herring as far as armoured company effectivness. As the superheavy rules stand now it is almost always better to have a lot of smaller tanks, just because they're harder to damage and can put out more firepower, all for
less points. And in games where it's actually reasonable to have baneblades you'll be playing with so many points that it isn't even that noticeable anyway.