USF doesn't have nondoc dive tanks capable of brawling it out with other tanks. Therefore the jackson has to fill two roles while most other factions have 2 tanks for the given role.
Either way if the jackson isnt good then USF wont be good.
it's not like the sherman wasn't there to be the meat shield for the Jackon's nimble glass cannon. You're going to add 160 hp to something.
late 1944-1945 sherman is different from the "tommy cooker" used in the african compaign. The US did improved on the model in the two years.
Even without going into the E8 model the US added wet storage, improved frontal armor, cupola, gun shield.
The US was also the only nation in ww2 whose tanker worn protective helmet as standard. Beret might look nicer but helmet save life.