If I understand you correctly, you think the base armor of Axis tanks is generally fine while the armor vet bonus is either not large enough or the Allied pen bonus is too large.
The thing is: Why should Axis tanks become better "tanks" (= eat more shots) while Allied TDs should not become better TDs? Not sure about the vet bonus percentages though.
For game balance reasons, I think a vetted Panther should be semi-reliably penned by a medium tank, so that a Panther can't steamroll the enemy if the enemy lost his TD (and it's relatively easy to outplay a single AT gut). Also, all TDs must be punished for being flanked, even by smaller tanks.
Also, running a TD into a TD should not be efficient for either side. TDs are best countered by AT guns.
To the StuG discussion:
Why not give it Blitzkrieg with vet or T4?
The problem currently is that the Stug gets easily wiped and that it does not quite have the mobility it needs to find rear shots at heavily armored vehicles. Blitzkrieg would help with both of that.
Let me explain this in numbers:
A Su-85 firing on Panther at max range:
chance to penetrate 220/260 = 85%
chance to hit 24*0.04 = 96%
Chance to do damage (hit and penetrate) 85*96= 82%
A Su-85 vet 2 firing on vet 2 Panther at max range:
chance to penetrate 286/286 = 100%
chance to hit 24*0.052 = 100%
Chance to do damage (hit and penetrate) 100*100= 100%
And keep in mind that Panther vet slower.
That means that balance relationship these units have at in vet 0 is disrupted at vet 2, for no good reason.
Generally speaking the armor bonus most Axis units get has lost most of its value due to the penetration values allied TD get. Same goes for target size since many of them also get accuracy bonuses.
Allied TD seem to overperform especially at range 60 with the problem increasing with veterancy.
It seems as most units seem to be balanced only at vet 1 and their balanced in other vet levels has not been checked.
Imo a veterancy overhaul with vet bonuses and abilities best suited for units is long long overdue.