Other OKW at options are IMO fine because they are supported by Schreckgrens.
As for Volks, in the AI department they already face similar problems as do conscripts in the lategame, ie. elite infantry (Shocks/Paras) or upgraded enemy mainline infantry (BARS, 1919s) walk all over them, turning them into little more than a meatshield/mp sink, while the actual AI damage dealing is done by Obers/Luchs.
3 Mp40s (!) like in Kappatch will not change that, at all. Its actually a downgrade, giving Volks less close range firepower than OH Pios and making them worse at all other ranges than in their status quo ante.
Flamethrowers might be a better idea, but I still dont see how this would amount to a solution. The problem is that the utility of Volks right now rests solely on Schrecks, and so does auxiliary AT for OKW. If you take them away without sweeping changes elsewhere, I am afraid its gonna break more than it'll fix.
OKW AT options are Raketenwerfers, Pumas, JPIVs and Panthers. These units are fine ATM (apart from the Raketen) and will be fine because Volks would get Pfausts. I actually think that Pfausts are better support for these units than Shrecks because they slow them down and thus make them easier to kill.
Volks will never face similar problems as Conscripts. They have much better vet bonuses AND they would get some sort of AI upgrade. MP sink is a bit exxagerated if you look at 23MP to reinforce (20 for Cons, 30 for Grens).
I never said that the AI upgrade they got in the Kappatch was a good idea. I didn't like it at all.
I'd give Volks 2 AI upgrades:
1. 1x Flamethrower for 60MU
2. The Grenadier Kar98s for 60MU
I'm not sure whether Volks should be able to use both at the same time or not.
5 Grenadier Kars might be a bit too much DPS if you take the amazing vet bonuses into account.
First, I would make Grens a 5 man squad. Then I'd adjust the damage of Gren Kar98s so that the squad DPS doesn't change.
And then you could give Volks the same weapon as upgrade.
You could decide whether you want a 5 man Gren squad with much better vet bonuses and no further weapon upgrade
OR a tool to clear houses.
I'd also play with the idea to give OKW 100% ammo income again.