I would also suggest more practice with the Katy, at the very least it'll force a retreat and at best end those super-super-super-glorious vet III+ Obers who would otherwise melt any infantry in your arsenal. The Katy is the closest thing to a reliable counter in the Allied arsenal for the reasons you've mentioned already.
I do not recommend Snipers as an LMG Ober can vaporise the model in 1 salvo.
Do NOT try to counter the deadliest AI inf squad in the game with inf, it's just going to bleed you to death in the long run. A good OKW player will bleed you from long range and counter dive attempts with a Blendkörper to really mess with you.
Source: Forum's resident Ober fan!
PS: Just press T if they're double LMG Obers.
