When the Sherman entered service, its mission, as assigned by the Army planners, was infantry support. Anti-tank was the mission of the anti-tank battalions. There is no doubt that the Sherman was not capable against the German MK V & VI tanks. Neither was the Soviet T-34. But in the quantities produced these armored forces were able to defeat the German armored forces.
You have to be careful which Shermans (and T34s) youa re talking about!
The Easy 8’s with the 76mm high velocity gun (British made I think) was much more effect against the Panther and to some extent the Tiger. Still needed multiple Shermans (Not as many!), and the high profile, thin armor was still an issue. How problem wasn’t solved until the Pershing.
The standard Sherman was disgraceful not only did it have the thin armor & high profile. Its low velocity 75mm gun was nothing more then a somewhat modernized WWI French 75. It was kept in production way too long due. People blame poorly thought Army anti-tank doctrine and even Patton for that decision. A lot of young men died because of that.
Slightly different topic: I read somewhere that the 90mm gun was available early in the war. Like the 88mm it originally was an antiaircraft gun. However unlike the 88mm US Army “doctrine keepers” successfully resisted early efforts to try it out as any antitank gun. Probably proper shells was also an issue. However eventually it was crossed over.
Again slightly different: Don’t know if the story is exactly true but its interesting. I do know early in the war we had no way of mounting a gun large then a 37mm in a turret hence the weird Grant tank configuration.