A single round of testing is not an accurate yardstick for comparing tanks, and your thread is not going to go far if you're going to constantly deflect to "the tests!".
Historically, 76mm shermans were actually left behind in England for the invasion of France. The 75mm was doing a good enough job against tanks, but it's turret had substantially better HE performance. It wasn't until the newer models of german tanks started showing up that US armor realized that "oh, we're going to need better AT guns on our shermans!".
You see the same dynamic in the game. Vanilla sherman is good enough vs a fresh OST p4, but struggles with upgraded armor p4s. E8 also preforms significantly better than the vanilla sherman against panthers and tigers, but won't solo them.
Rifle company isn't in the meta because heavy cavalry does everything it does and more. If you want to see more doctrine variety in USF then heavy cav shouldn't be some omni-doctrine offering the best in infantry via the rangers, smoke, sandbags, and mines, and also the best in armor via pershing and super zook rangers.
While I agree Heavy Cav is omnipotent, it isn't far removed from your average tiger commander for Ostheer, for example. It just has doctrinal elite infantry instead of nondoc.
E8 is signifigantly better at getting a single lucky hit in on a heavier tank than a P4, sure. Is it worth 30 extra fuel and the drop in AI firepower to be marginally less helpless versus a Panther? On the historical 76mm front; the 76MM Sherman has not only (MUCH) better rate of fire but also better AI profile for the individual shells. It's no P4 or M4A3, but it's a long shot better than the M4A3E8, while also having the APCR shell with better penetration and reload time than the M4A3E8, and all of this is without a power creep series of buffs towards it. (The unit is so untouched it retains the borderline absurdly overpowered ROF from its Soviet days, which couples nicely with vet and radio net)
Not to mention the E8 is in arguably the worst USF commander, with most of its abilities being medicore or just useless.
The worst USF commander is Infantry. Rifle Company is actually pretty good now imo, though I agree it is overshadowed by Heavy Cav, in great deal due to the heavy tank buffs.
You did a test once. And EZ8 still won. P4 pens EZ8 around 50-60% of the time 5 penetrating shots are needed, while EZ8 pens 70-91% and 4 penetrating shots are needed. EZ8 has 0.75 moving accuracy as well. I believe P4 has a slightly higher RoF. These are significant advantages that make EZ8 a hardcounter.
If this is your definition of hard counter, you may as well say the P4 is a hard counter to the M4A3 or T-34/76.
Victory against a P4 is as much RNG as it would be for the P4 to beat the E8. It is hardly decisive and hardly a "hard counter". This would be more along the lines of Panther vs M4A3, or Panther versus M4A3E8 for that matter.
I'll do a whole 'nother series of tests if this is not convincing to you people. If I can figure out how to record on this machine, even produce video.