The Tetrarchic portraits are all military in nature, Diocletian was a barracks Emperor, --so strong, thick necked men with close cropped hair and beards. They also look alike, probably, in an attempt to reassure the people...this new ruler (insert name), looks assuringly like the other guys-- continuity is assured.
Well the whole history of Rome is militaristic. Isn't Julius Caesar a military man? Isn't Septimius severus a military man? How come these guys did not show portrait of a thick neck man? Only from around 290 AD we start to see this feature?
Styles change...a few years later, beards are out. Plus this is Diocletian's Tetrarchy, his "vision"...his style.
I don't mean to nitpick, but was Hercules a god or a demigod? If he was a demigod, was he claimed by Maximianus or was he assigned to him by Diocletian to reinforce his secondary status?
Yes, Hercules was half-god, so lower in the pantheon than Jupiter. I don't know whether or not Diocletian assigned Maximianus to Hercules; but Diocletian picked number one Jupiter for himself, meaning whether Maxiamianus picked for himself or not, it didn't matter, he was by default getting a lesser god. Diocletian was in charge and Maximianus knew it. This is further reinforced by the workshops of the coins I posted-- Diocletian is A -- alpha and Maximianus is B-- beta.
If I were Maximiam, I probably would have picked Mars as my patron as protection from and as a warning to any potential invaders or usurpers. Hercules seems much less powerful. That's why I wondered if Hercules was Diocletian's suggestion/assignment.