AA units OP?

[Helsingor]

Anyone else feel that AA units are too powerful defensively vs. infantry? I understand their defense value vs. tanks (the German 88 mm was of course originally a flak gun that proved to be a great tank killer, and I think there were similar examples in other militaries), but can't tell you the number of times I have attacked an AA with one or more Armies and gotten meager or no results. Supply and Entrenchment levels don't seem to make a difference. I know that at this scale, there is a level of abstraction and an AA unit in SC: WaW should not be thought of as merely a bunch of flak guns, but still they often seem better at defending key points than Armies or Corps

Is there something I'm missing?