The panzer 4 should have weaker armor and more powerful gun.
historically the panzer 4 had weaker armor than the sherman and t34/76, unlike it is portrayed in game.
the panzer4 had 50mm of armor on the turret + 80 mm of armor on the hull. This was thinner than the 90mm of armor on both the hull and turret on late war sherman and t34.
The cromwell, meanwhile, was roughly equivalent in terms of armor to the panzer 4, with 76mm on the turret and 62mm on the hull.
This present a interesting situation, as it means the three factions with advanced medium tank (panther and comet) also fielded regular medium tank with thinner armor than the two faction with only one medium tank (USF, SOV).
focusing more on the panzer4, the main reason it had thinner armor was in large part due to its gun. The 75mm kwk40 was an very good gun on par with the US 76mm and Soviet 85mm, but mounting it pushed the pz4 chassis to its limit.
This was an acceptable trade off for the german, and the more powerful cannon allow the panzer4 to remain competitive with the 75mm sherman and t34/76.
Currently in game, the panzer 4 's combination of superior armor and gun allow allowed it to tackle the USF's sherman comfortably, when in reality the late war m4a3 75w was a formidable match for the pz4. (the t34 had other issue, the cromwell was similarly thin skin with a weaker gun)
With the presence of the panther tank in both the wehr and okw tech tree, the panzer4 need not to be dominate against the t34/76 and the sherman.
The panzer 4 should be a thinly armored vehicle whose greatest strength is the flexibility of its firepower. Its firepower would allow it to fight comfortably on the defense, but its thin armor make it vulnerable on the offense. In late game the panzer's firepower make it an effective flank protector for the german big cat.
Here's my proposed penetration and armor value for the wehr panzer4:
penetration: 140/160/180 (current 110/115/125)
armor: 140
AOE, reload, and the mg would remain the same.
- Pz4 has 50mm of vertical armor.
- Sherman has 90mm of ANGLED armor. (or was it 65mm of angled armor?) I forget.
So the difference is even bigger than you think.
(Mind you, a later refit tacked on +30mm on both Pz4 and StuG front armors)