That's not what I meant to imply. The 75mm Armed Shermans did fine when used in the roles you described. Most Armies used Tanks to fight other Tanks, the US Army felt that this was the role of Tank Destroyers, and thus despite the introduction of the 76mm Shermans, the Army felt they were unnecessary. The Army felt that a Tank could choose to attack wherever it wanted, and that a Tank Destroyer would respond to enemy attacks.
It wasn't until the Battle of the Bulge that the Army realised the Tank Destroyer doctrine was flawed, and that a sudden blitz through their lines left them unable to effectively fight back with Infantry and Shermans. It was after this realisation that the Army ordered all future Shermans be 76mm, and that 75mm Shermans will no longer be accepted.
Yes, I believe thats true. The reasons the Shermans were kept with the 75mm I believe was due to the insistence of the General of the Artillery who also slowed down M26 development.
In CoH2, the Shermans (excluding the E8) can do AI efficiently and AT as efficiently as a Pz 4 H, but struggles against Panthers, Tigers and Elefants, as they should.
As you find in CoH2, save certain exceptions like Pumas, AT Guns (the latter which I'm fine with because there's a far greater risk in fielding AT guns than there are vehicles), most vehicles end up playing out reasonably truthfully to history, aka, the kind of performance we'd expect out of them. The only big gaping exception at the moment - is the SU-76.
And if the SU-76 can deal with German Midgame units, I'd definitely build it, it would easily shut down Pz 4 options that they otherwise could bring along and thats a big thing as it forces people to tech to Panthers.