I disagree with the stun.
By all means, the HBG is a normal satchel (just tested it, does the same amount of damage, same fuse, same range). The HGB costs 5 mun more though.
HGB has a range of 12 and can keep vehicles immobile for a very long duration.
A normal satchel does engine damage if the vehicle does not drive away, the HGB only does a stun. So actually you pay more for the HGB and get less, at least AT wise. Don't know about the exact AoE damage profile, but I assume they're very similar too.
You should not use the Penal as the benchmark because their are badly designed.
You also seem to underestimate the long immobilization effects and possibility of "stun lock" especially if the weapon becomes homing.
Finally have even less reason to compare it to Penal because my suggestion is either to be moved to Ro.E. or to become a homing "soft snare" for IS.
And the Penal satchel does NOT cause gameplay/balance issues.
Penal do not have access to smoke or to HE grenades.
I don't see why this topic should be an issue at all. The only combination might be smoke + HGB, but that is probably a smaller issue that can go live. Balance team has more important things to sort out at the moment than this, so the time can be used elsewhere way better than on this single combination where at least I am not even sure if it will cause problems at all.
Imo patch team (Relic and MOD) have spend too much time fixing the "important" things (and then having to fix them again and again) and far less fixing smaller thing that could improve the game allot and are "easy" and "safe" fixes.
The change is simple and easy. Simply revert AOE damage changes, keep the munition reduction make the weapon homing and remove the affect that make the vehicles immobile or move its Ro.E and remove the immobilization.