Let's say this particular example, Overmatch, failed to hit the fuel tank or the ammo storage. Should it not be a kill anyway? Or produce much more damage inside the tank. Even if the crew was able to survive, inside it would be hell. And they would all leave the tank to survive.
Depends. Non-vital penetrations should probably have a higher effect on the tank, but at least some of the crew are likely to survive those non-vital hits, and it's possible the tank will remain in action. It happens. Penetration doesn't mean an automatic kill. Which is good, because in reality, both of those tanks should be penetrating the other on almost every shot.
And the Russian one, would be ok to damage the Panzer IV, weaken it's deck or something.
A hit atop the turret would burst the armor right above the heads of the commander, gunner, and loader, which I can't imagine would be good to them. A hit above the engine deck would likely cause serious damage to the engine, and might even set a fire. I don't think it should be an automatic always-one-hit-kill, but it should have a chance, and should certainly do damage.
If a russian 1kg grenade can a chance of killing the Panzer IV instantly, why does countless HE rounds from the T34 would not do the same?
Because HE rounds vs. tanks are weird. The two are coded differently. They seem to do hitpoint damage. But you can (...eventually...) kill a tank by pounding its front with HE rounds. Might take you around ten or so... (Considering the results some people are claiming about shooting the T-34, I would almost think they're using HE)
And how come the F34's AP can't even do the same?
...can't what? Do a one-hit kill? It can...
There. This is what I am talking about. This is the wrong approach! Instead of making the ATR stronger they should make the tanks less frequent! And the 50% should also be revised.
Okay. If we want to make tanks a realistic rarity, so that tank power and infantry anti-tank power is equal to the historic balance, we should get one tank every... Three rounds, or so. Not one tank slot, one tank.
If you're going to have tanks more often than that realistic frequency, you're either going to have to scale up the infantry's ability above realism to deal with them, or else you're going to have a scale of balance that's far off from realism.
How much of the 1kg-grenade was actually explosives?
Looks like 760 grams. The charge is made so it detonates flush against the armor (Ideally), and can burst through 20mm of armor, and causes spalling through thicker armor.