So make even more further changes to other units, just so one change would make more sense?
You're confusing armour and armament. The latter you have not one, but four options. USF doesn't need a fifth just because someone wants to stick to Shermans.
In terms of armour, I believe the COH2 Churchill variant is about 110mm think, a smidge above the Jumbo's 4in. KV-1 has 90mm. If we're going to make them scale, then Jumbo would have to perform with the damage soak of Churchill. Which means hideous imbalance given what USF has. You're better off letting them make King Tigers.
I don't even know what the hell you're talking about.
Back when the USF was the Allied underdog it had shit everything, no terminator vet 3 for Rifles, no mortar, no nothing, they were an extremely micro intensive Army with shit almost everything.
And their tanks are still shit, this time around however they have superior infantry and support compared to everyone else.
And before the Pershing, talks of the Jumbo and up-armored 76mm Shermans were still going on.
And I still support the idea of having an upgrade to upgun the Shermans and getting a Jumbo in the game via a commander for the USF, the USF just needs more meatshield tanks in order to protect their Jacksons which are very fragile glass cannons on tracks, and the Pershing doesn't really fit that role, but a Jumbo would.
As far as the Churchill goes, I am not sure where you got your information, but the Churchill variant in the game, the Mark VII had 175mms of armor, that's more than the Tiger tank, you can read more about it here:
https://en.wikipedia.org/wiki/Churchill_tank#Tanks
Of course there is info on that outside of Wikipedia but I'm just too lazy to go get it.
The Churchill Mark VII was the most heavily armored Allied tank of the entire war I believe.
Anyhow, both Soviets and UKF have their meatshield variants of tanks already in the game, Brits have the Churchill, and the Soviets have their KVs so I don't see the problem of nerfing the USF infantry and giving their tank force a bit of a buff in order to balance things out.