To be honest this new idea doesn't seem bad. I would think it will be very similar to incendiary barrage of the Soviets plus wasn't flame damaged nerf years ago?
This has to be a joke of an opinion since the OP doesn't even have the Brit Army to play with. I would take Falls over Commandos every time (Camo + Faust)!
Solution
That being said: Brummbär needs its old range back and a tiny front armor boost.
I do like the idea of buffing Brumbar's range again but damage vs vehicles needs to be nerfed. I think the major problem back in the day was T-34s and AT combined arms was struggling hard to kill Brumbars. If Brumbar needs to counter static game play such as AT guns then damage vs vehicles needs to be toned down and make it strict AI vehicle.
Another idea I was thinking to counter Allies LV is to give Puma as a non-doctrinal unit to Wher. I know one commander will need to change but this will greatly help with 3 v 3 and 4 v 4 games as well where T-70 is rampant!
Balance wise I think its fair with minute nuances. The major problem plaguing the large game mode is matchmaking. Majority of the time if you play any game with your friends that have over 3k hours you still end up fighting noobs for 10 games straight. Its incredibly boring unless you play with same people for 10+ games.