The problem with the ML-20 is how devastating it is per shot, not that it fires to fast. A 1 or 2 shots on a OKW HQ truck can easily wipe a shitload of infantry. The ML-20 just needs a damage or AoE reduction. Better yet, OKW needs an actual counter to it.
Replacing Valiant assault with a recon sweep and air assault with a ME-262 bombing strike would work fine for getting rid of howitzers.
I've devastated 16 infantry models(11 cons and 5 shocks) with single rifle nade last night.
No AoE reduction will help if you blob or mass retreat, this is the punishment for bad play.
LeFH does exactly the same to allied infantry when it hits them.
The damage matters only against armor/structures. If you'll get a hit on infantry, it WILL die.
If you have clumped up infantry when the shell hits, well, maybe you shouldn't blob so much(i know its your fav playstyle, but the arty is intended hardcounter for it), maybe you shouldn't mass retreat?
Because there is nothing that prevents you from repairing your trucks between barrages.
On a related note-how about we made it so sturmtiger can't wipe any inf unless it directly hit the squad in the middle? I don't see how anyone complaining about ML-20 and B4 before would not be in support of such change.