Profile of Mirdarion

This was because US tanks had stabilizers that assisted in firing on the move, a feature unique to them.

No, this was done because the Sherman in the game back then was significantly worse than most other medium tanks it faced (its anti-armour performance was close to the T-34/76 without being as cheap). The price on the Sherman couldn't be lowered, because it was primarily meant to be an Infantry Support Tank, which is why it has such highly effective (against soft targets) HE shells. So the balancing idea was to enable the Sherman to fire on the move with more reliable accuracy, in order to enable flanking strategies (this is supposed to work together with the Radio Net passive upon vet1, so that a group of flanking Shermans gains some massive firepower buffs, that would otherwise lead to incredibly OP situations if done through normal buffs).

There is no realistic base for this, as even the (by today's standards) primitive gyro-stabilisation used on Shermans didn't allow the tank to fire on the move. It "merely" allowed the tank to acquire its target while moving and thus reduced the time standing still (and presenting an easier target). Shermans still couldn't be fired properly on the move, especially when travelling cross-country - that technology wasn't available until the '70s with the combination of fire solution computers and modern gun stabilisation.

I said "SOMETHINGS" not evrything, look games like age of empires 16 years older and still well balance

Well, then you naturally have to explain the reasoning as to what is equalised and why. Otherwise we would have to call that adjustment the "Arbitrary Balance Patch" (which is a cool name, I have to admit). As I said, the system itself is not free of flaws, but there are significantly easier ways to fix that, rather than reworking the whole teching structure. That would of course require quite a lot of research into whether those teching structures are actually as broken and/or one-sided as you make them out to be, because these changes have massive implications by their very nature.

Maybe give the soviets free upgrade but lock it to tiers like Osther :/, somethings must be equal i think if we want balance

By that logic we would have to lock the Lieutenant, Captain, and Major behind extra payments, because no other faction gets units essentially for free with teching. And of course that would require the removal of the FlaK on the Schwerer Panzer HQ for OKW as well (with the medics and repair pioneers having been adjusted already).
While we're at it, all factions should also have five-man infantry squads, remote weapon upgrades, linear teching, etc. pp.

Do you see the problem here? There are already significant differences in terms of teching linearity and teching costs to make up for the differences in side-teching (there's of course also the timing aspect, especially with Ostheer having to research and build a teching level), so how about taking a look at these first before adjusting the teching structure itself?

This is like the debates about USF and OKW flak gun and 'free' teching.

That said, there are some significant imbalances there. For example OKW doesn't get free medics and free repair pioneers with their teching anymore, or that the lack of side-teching for Ostheer barely counters the effects that the cheaper and faster teching with "free" units of USF have on the gameplay (getting direct access to snares instead of needing veterancy for that is barely countered by the free forward retreat point the Major offers, for example - especially as later on these teching differences heavily outweigh the side-tech costs).
A lot of that is of course really complicated to depict properly (making Gren MG 42s a side-tech would lead to massive problems in tech pacing for Ostheer - even worse than it is - as their core infantry doesn't work without those MGs - they are not a strategic option, they have to be upgraded in order to have any hope against other infantry).
There's also the argument that sideteching increases strategical diversity, by allowing for different strategies through tech-rushes for examples. This hardly works for some factions, as the teching costs are still (even in the current WBP) massively fucked up in favour of certain factions, not to mention that the teching structure itself heavily favours some factions over others.

The biggest problem here is the scope of that imbalance. So many things tie into this, that it is virtually impossible to correct even small mistakes without creating even worse problems in other areas (or even in the same area). That is why the OKW medic system is so fucked (especially if the WBP idea of locking the 251/17 behind medic tech goes through) and is in dire need of a rework (again), because it in no shape or form is a fairly adjusted investment - especially as it is basically not optional, considering the ridiculous ammo drain of health packs and the manpower bleed suffered if a player ignores healing.

Penetration should go down for "medium tank" destroyers Su-76, stug, M10.

Again, the StuG is not a tank destroyer, it's an assault gun. That difference shows, as of all the vehicles you just lumped together, the StuG is the best performing against infantry in general (the SU-76's barrage excluded). Throwing especially these three vastly different vehicles into the same pot (especially as the M10 is about as problematic as a stain on the sole of my shoes) ignores the necessary delicateness required to actually balance anything in this game.

Increasing the accuracy might require increasing the fuel cost a tad. Like 135, if we are talking about about %75 and up.

This is actually my less preferred method of balancing. That said, the problem is similar to the formerly low target size of the Cromwell: It shouldn't have existed to begin with and the fact that it is shows a clear lack of understanding into the game's mechanics and how they actually play out, on the side of Relic (which is kind of ironic, considering the created this game).
Back to the problem at hand, the Cromwell should have never started out with higher moving accuracy. It has the proper penetration to not need to flank, or at least when doing so, it is far better off than any other medium tank even without that accuracy. People called the target size correction on the Cromwell a "huge nerf", when in fact it was simply brought to the same standards as all vehicles in its class. If the accuracy adjustment is also a big nerf, then I'm wondering how the Ostheer Panzer IV could even remotely be considered as useful in any way.

That isn't a bad idea, but the Cromwell is the only unit in need of that treatment IMO.

No, as it stands by now, the Sherman got buffed to the point that the Panzer IV struggles against it. Sure, you could always go for StuGs, but you can't do both at the same time (not with those fuel costs). And that's showing the problem of generalist versus specialised units, again. One way to avoid that would be buffing the Panzer IV, but that's the bad option because it puts the StuG in a weird position (especially as we can't buff the StuG any further without it becoming OP). This is the Sturmpanzer (Brummbär) problem all over again: No matter how much you buff the StuPa, it will never be worth it unless you make it OP, because it is the wrong tool for the wrong job at the wrong time.

P.S.: To further iterate on that, re-evaluation of the moving accuracy of all tank-fighting vehicles (assault guns, tank destroyers and tanks) should be done. That way we could further solidify the defensive role for example of the StuG and SU-76, by actually giving it an even worse movement penalty (although we would have to find a way first to prevent turning as being interpreted by the game as moving, otherwise its turret-less design would be far too problematic).
That could also serve as a good solution to the above-mentioned problem of the identity crisis going on between StuG and Panzer IV, aside from what we have now (slightly different AT performance and range).