The Sherman is a good all around tank it probably as cost efficient as PzIV.
The 76 Sherman will beat the PzIV.
If you USF have a tank that can engage the Panther (which is designed to counter tanks) 1vs1 and win then Ostheer would simply be lose badly to USF.
USF already have better infantry, about the same Support weapons, better light vehicles about the same medium tanks and more cost efficient TDs, giving them a premium medium tank able to 1vs1 Panther would simply make them beat Ostheer at all stages of the game.
But they'll still be lacking rocket arty, sniper, cheap tank destroyer and brumbar like unit. In definitive you're just over exaggerating USF capability and over underestimating Ostheer ones.
Where I agree with you is that the Ez8 doesn't need to be changed, picking the doctrine doesn't restrain you from building a regular sherman or a scott for the AI purpose and keep the EZ8 to face other tanks.
What the doctrine needs is a removal of the sprint debuff or better, making it equal at Ostheer one, all infantry except atgun and pak are running faster for a period of time.