I go with a soviet opener of 2 cons and a sniper to counters Assault Grens. Weak at first, but gets going once the sniper makes some kills. Mostly to show the new German units aren't that hard to counter. I used to mini field gun for light-AT work from the new Urban Defense Tactics Commander.
This game was not so much "how to counter A.Grens" as it was "how to lose 2 flamehalftracks badly". I think the skill difference in the game nullified it from being about balance much. Soviet T1 definitely seems to be the answer to A.Grens and the 45mm AT gun call in is a great response to the inevitable German scout car that comes to counter Soviet's T1 response, so the game still had some useful things to see.
An M3 will get crushed by a German scout car. Given that Germans don't need to build T1 with this strat and can go straight to T2, a scout car can easily be out to meet the M3.
I used to mini field gun for light-AT work from the new Urban Defense Tactics Commander.
Enjoy.