Completely aggree with your statement but not with your solution. We may see M10 being spam as hell for that price like the Su-76 at his shiny time.
On one hand, I think this isn't necessarily a bad thing, but on the other hand I understand that people seem to recoil at this kind of gameplay. The SU-76 is a little different due to the fact it is not in soviet T4, and it has the free artillery barrage. A few SU-76s can wreak havoc on team weapon positions and chokepoints, unlike M10s. (Though M10s can do some decent crushing.) I think they're sufficiently different, but you do make a point. I just believe that the lack of AI on M10s leaves them particularly vulnerable to paks and raketens because they cannot just shoot the crew down, throw a grenade, or launch an artillery barrage.
Imo, a weaker M10 should be available after two tiers unlock and be individually upgradable to match/improve their current stats.
So when the first M10 hit the field it is not an insta hard-counter for every mediums, leaving room for the Axis player. And the upgrade becomes mandatory to keep it relevant but also to prevent spamming them.
If this is how M10s are locked by tech, then yes, they shouldn't be an insta-hard-counter on mediums. If they are not to be tied to Major tier, then their current cost may even still be appropriate.
I'd support reducing the M10's cost to 300MP 80FU, removing the HE shell, and see how it performs from there. 70FU rivals the Puma and I'm pretty sure the M10 is more effective than the Puma; it would be far too cost-effective then (You could get 2 M10s for 1 OKW P4).
This is indeed the biggest caveat: OKW tech design and that they have a P4 in their FlakHQ. (Also the fact that OKW has non-doc KT which means there's always a threat of heavy armor.) This is why I had the suggestion of adjusting the penetration on the M10 to pressure closing the distance for effective use.
But a fuel cost of 80 may be more appropriate given the costs of Pumas and P4s. There's just very little room to adjust fuel cost before the M10 becomes too expensive. Maybe 75 fuel.
I'm just not sure even 80 fuel is cheap enough to make an doctrinal major tier M10 a better option than the current Jackson.
I'd love to see this, but the issue is that the USF would be doctrine-reliant on dealing with Axis heavy armor. Doctrines with no answer to Axis heavy armor would fail to be of much use (e.g. Recon Support, which has no late-game units/abilities).
Perhaps, although such improvements to the M10 would mean USF would be able swarm with M10s against heavies, much like they were before the M10 was put in Major and the Jackson buffed to the hilt.