How on earth would rifle grenade kill combined arms experience, when Darkest Hour has one of the best combined arms experiences even though there are Panzerschrecks present. I used to kill tanks with it at 150-200m.
And rifle grenades wouldn't ruin the experience any more than PTRS, which penetrates sides of Pz IV with ease, can kill optics/damage cannon and is semi automatic.
Rifle grenades can only penetrate T34 turret front at the 0 degrees angle, or front armor if grenade arc is big enough to minimize the front armor angle effect by 20 degrees or if shot from higher ground. It's less accurate, has low range (up to 150m), takes long to reload.
If GrB 39 was in game germans would have specialized AT weapon, with better penetration/destructive effects than PTRS, but much much slower firing, less accurate and with much shorter range.
To me it seems pretty balanced.
With PzB 39 we have a door knocker that can't do **** against T34, which is going to be the ONLY soviet tank at the game release. So we're basically without any ranged infantry AT weapon. Not a good situation when russian tank is at the crossroads firing at your positions 100m away.