Locking unit performance behind a timed ability costing munitions isn't the same as a one-time fuel cost. All the enemy has to do is disengage for X seconds and that's munitions down the drain. It's also why the M36 is so much more attractive and ubiquitous in USF builds, since a M1 ATG simply isn't reliable versus heavier axis tanks (whereas it is incredibly capable versus lights and medium tanks).
The Jackson doesn't much equate either for the fact that it's the end-game AT option for USF and essentially has to have good penetration to compete with end-game armor of axis factions.
I have said before that one can look at ROF or moving accuracy or some such with regard to the M36, but penetration is a very, very strange place to look when considering nerfs for this unit.
If the enemy was in a situation where they can just back off it didn't matter anyways, and even then the usf AT gun is in a better position than any due to its increased rof as well as its increased range with vet. And even at that, if the enemy just says "yep this is a no go zone for 30 seconds" the AT gun did its job.
Having a munitions cost for scaling is fine as long as it's not locked entirely behind vet (this is where the Jackson design of old failed). Munitions is one of the 3 resources you earn in this game and is greatly overlooked in the balance. In this case it let's the cheapest stock at gun around become the most powerful. Which is a good thing for munitions to do. The munitions points should be fought over with as much tenacity as the fuel points and the effect on the late game should have the same value (conversion rate allowing)
Also the Jackson is simply over powered. It has the power sit and plink or chase. It has great pen and accuracy AND an ability to increase it further, but also damage because fuck you! MURICA! It defies balance. But that's a rant for another place.
Munitions are in a strange place where they are a passive thing instead of an active thing and they should be the heart of the dynamic play, not a side line attraction. Buying a weapon upgrade shouldn't be a no brainer, you should have something impactful to weigh up against. If the Jackson had HVAP no vet and it did as it does now, and say Sherman HE was an ability instead of a passive perhaps double rifle blobs wouldn't have been treated like the norm and gutted to the level that you need 2 for any meaningful impact. Choices. I guess what I'm getting at is a lack of choices when it comes to munitions.