Hey hey Pershing really isnt that bad, its biggest weakness was low power/weight ratio. In all ways (except character) its equal to superior vs Tiger 1. It has advantage over Panther in side armor thickness, although its all vertical, and most of all in shilouette, Pershing is actually pretty low slung and has excelent profile. Frontal armour is 100mm at about 45degrees.
As for the M3 90mm gun its at least equal or better than the awful Soviet D25T 122mm as far as AP is concerned, the 122 was barely equal to Panther's KwK43/L70 in AP. The Soviet 100mm was a better gun but only mounted on SU100 during the war or as field artillery.
As for preffering a 76mm M4A3E2 Sherman Jumbo over Pershing, think these facts over: Jumbo is actually slower 22 vs 25mph, it has much weaker gun HVAP or no HVAP, M3 90mm had it too, its less realiable, has higher shilouette, both had same frontal armour but Pershing is much smaller target, and Pershing is also much better in HE.
In RL Pershings had trouble in Korean hills due to low power/weight ratio, so a standard Sherman was often preffered especially after the T34/85s were less common.
The IS2 is an interesting tank, the big 122mm gun had poor AP performance for its size. The tank only carried 28 rounds of 2 piece ammo, which hurt it in combat as it slowed re-loading and had short ammo duration. The 122mm had great HE capability fring a 25kg+ shell. Frontal armour was about 110mm mostly vertical on the early ones, and side was about 85-90mm. Shilouette was the best of all relevant heavy tanks (IS3 doesnt count), its really low and narrow. It had the usual soviet low quality optics and ammo which hurt a bit. Overall it was good for what the Russians wanted it for in WW2, but not too useful in AH due to very low ammo count (considering 75mm and 88/90mm can do better and have much more ammo- Panther has 80-90 75mm).
T34/85 would be good in AH, or a nice late ambush painted Panther Ausf.G with the chin mantlet.
BTW Pershings weren't widely used after VE day in the Pacific, they just had a few of them in the very end of Okinawa and they did pretty much nothing.
