I can't tell the difference between a short-barrelled 76mm Sherman and a Jumbo. What am I missing?
There is no short barreled 76mm Sherman or Sherman with a 75mm gun equipped 76 turret tank.
The 76's turret was used because of it's increased weight limit, that's why the Jumbo used it for the increased armor.
So unless you put your glass on and zoom out all the way in-game in the middle of battle you will not notice the lack of literally 1mm of the armor on the model and can't confuse it it with the 76 Sherman.
Whoever has at least a basic knowledge of WW2 and American Armor, which includes Sherman variants for the most part, will be fine with a shorter barreled 76 Sherman with a different icon and text.