My proposal would be to lower the reinforcement cost to 26, increase their cost slightly while decreasing the mp cost of t1 slightly, to compensate for this i'd increase the cost of grens to 260, buff their mid to close range so they don't have to retreat the moment you get close
This is a working solution and I agree with the whole post. The only issue I see with it is that buffing the close-mid range isn't quite in line with the theme and overlaps with the assgrens. I would rather see their long range kar98 damage buffed so they would be competitive option for ostruppen on open maps. You are always gonna go assgrens on close range maps anyway.
EDIT:
I also think that it is a ripe time to revaluate the T0 and T1 design when it comes to building grens and HMG as one piece of this "make grens viable again" -puzzle