A shrecked volks blob can do what? Vaporize any infantry and tanks. Yes, it can if you just yolo rush your tanks into it. Volks can also fight inf but what if...I don't know....what if you use anti blob weapons such as (off map)arty, demos, mines or any other form of indirect fire (that's also a counter to Obers btw).
If you are talking about Obers + Shrecked volks. Well, Volks are AT and Obers are AI. That's "combined arms" to some extent. So, you obviously shouldn't simply fight them directly. If it's a blob it's even better.
It's still inf, so you can use all the stuff I've mentioned above. If there's a Panther + Obers + shrecked Volks it's more difficult. You have to use combined arms yourself then.
The thing is that combined arms from Allies are far less effective than "combined arms" from OKW, if we can call that combined arms. To me, it is the same than a bioball from Terran in Sc2. A blob easy to do and that can rape everything with ease.