If it was realistic, they wouldn't score direct hits all the time in the first place. Also, we are not talking bombings from 1500 planes here...
They don't. A bit of panick and one HS 129 turns very innacurate.
If we start lowering down the accuracy of HS 129 or other planes i fear you'll have to bring other at/armor assets into infantry decks having them as at response. Turning infantry decks in something else than infantry in the process. I feel they are fine right now, maybe deadly in A but very fragile against figthers due to their speed. Decks like 101st airborne/6th Airborne have assets to bring them down.