While I agree with the general idea of what OP is saying (insane vet is insane), it's really only terrible when playing as Ost. Grens get brutally outscaled, to the point where they become incredibly hard to use.
Just look at the stats:
Grens: 4 man squad, 240/30mp, 1 purchasable upgrade slot (Long AI)
Rifles: 5 man squad, 280/28mp, 2 purchasable slots (AT, Close AI, Long AI)
Infantry Section: 4-5 man squad, 280/28mp, iirc 2 purchasable slots (AT, Long AI)
Conscripts: 6 man squad, 240/20mp, 2-3 purchasable slots (3x PPSH, 2x PTRS)
Early game, yea, their survivability isn't an issue do to very high long-range DPS (except vs. tommies), but by late game, they're insanely weak. Losing ONE model cuts DPS by 25% (vs. 20 to 17% for everyone else), they can only buy one upgrade (and pick up a second one) vs. everyone else being able to buy 2-3 and their upgrade is ONLY good vs. Infantry at LONG range (vs. AT, Close, medium and long AI).
Add to that the AI's tendency to group up making the 4 models much more likely to take heavy losses to AoE (in terms of squad %), resulting in a quicker retreat (less models to lose), and a higher reinforce (why!?), they end up getting pushed around a LOT by late game.
Seriously; try it. Get a vet 3 1x LMG gren squad in yellow vs. a Vet 3 2x BAR or M1918 rifle squad in yellow and see what happens. MP cost they are 7.7% more expensive per model in initial cost AND reinforce per model; but they'll lose every single time (the base cost on rifles gets you an extra model and thus more HP).
However, IMO, the solution isn't to nerf vet (although some of it needs to be looked at). Instead, gives Grens a "bolster squad" upgrade that simply gives them +1 model, and +1 purchasable upgrade slot (so I can buy a 2nd LMG).
Luckily, you don't have to rely of grenspam to deal with lmg rifles. The lack of grenades with these units and the very low on the move dps make the LMG rifles very vulnerable to the HMG+sniper combo.
Also why do you completely neglect G43 upgrades but put PTRS up as an upgrade for conscripts?
As for your solution: 5 gren double LMGs would be insane. They would vastly outperform double lmg rifles despite being cheaper to buy, cheaper to upgrade, and require no doctrine to get. USF also has no snipers or any elite infantry to counter them. They would also walk over Soviets, who not only have no stock elite infantry, they also do not get stock weapon upgrades. Their sniper is also not that good compared to the Ostheer one.
But seriously though: Wehr has the counters to 2x LMG rifles. Giving them the firepower to just straight up kill the most expensive infantry squads in the game with their own basic infantry will just wreck balance and cause even more power-creep.