Sherman does to Pgrens what Tigers/P4s/Stugs to a lesser degree/Brummbars/Luchs/Ostwinds do to Bazooka squads. I see no real issue with this. The Sherman being what the Sherman is defines the USFs core advantage. Flexibility.
The Sherman is best at AI. I would classify it personally as an AI tank. Thus not cost effective to counter with Infantry. And the sole reason its justified Pound for Pound Axis tanks have better armor and AT ability.
If the Infantry vs AI tank Meta needs to be adjusted then Zooks should be looked at I would think.
Tigers deal with infantry pretty well, but that's a late game tank and very expensive (are we already comparing Tigers and Shermans?
), and allied infantry are less susceptible to insta-wipes because of larger numbers. I have to disagree with you about PzIVs and StuGs do the same thing with Bazooka squads. Although they do sometimes perform crazy wipes, that's because of the cover system, we can check stats and compare them. As you said, USF should be flexible by design, but Shermans counter medium armor and infantry with ease and they arrive quickly, so the USF player gains huge map control (Remeber that we are talking about USF vs Ostheer). I've always been a fan of "reduce damage increase AOE" regarding all of Explosive Shells (Shermans, Brummbar, TrolStuka, ISU etc.)
Your point about Bazooka is valid. That thing is pure BS, not only you have to spend muni, you lose significant amount of firepower. Need slight pen increase and damage, so you can actually rely on your Bazooka squad to hold Medium armor at bay.
I don't know how can they fix this situation, because USF relies on Shermans and they decent HE damage versus OKW. Against Ostheer though, I'm not sure what to do.