Normally, I attack in front using smoke to cut paks and mgs (as for allies, I usually play USF). To counter these guys, there should be also rifles in 1:1 proportion backed up with HMG or Stuart. And this is only to counter Knights with Paks. But later there would be tanks and situation will become silly, because:
Well, how do you normally counter AT, and AI? That should be the same counters for these units. It's not like they can camouflage, and even if you manage to kill 2/3 men while the last one retreats, it's still 170 manpower to reinforce 2 of them. As for the railway artillery, it gives plenty of time to move out of the way, so the only effected units should be static ones. It's more of a breakthrough ability, that it is artillery. In my opinion, it encourages to not build emplacements close to each other, therefore less sim cities.
Ost Knights > USF Infantry
Ost Tanks >> USF Cardboard
I am always against an superexpensive super units, because they are nearly impossible to balance - they will either suck or punish almost everything (any infantry count as well) for little effort.
Air Superiority was nerfed because it had a great CHANCE to destroy single full HP OKW truck. USF artillery barrage was reworked for almost the same reason. I guess, artillery that is able to destroy several full hp braced emplacements which cost mp and fuel would be nerfed before these two, if it ever existed.