Game designing takes a certain amount of creativity. That's something a lot of people fail to see. If they want a healer, they can make a healer. They can make a demon/monster class without making it anima.
As for no guns, I don't see why. Diablo 2 had the cutlass and saber sword which didn't appear until the 15th and 16th century, while the muskets were in China in the 14th century and firearms were there even back in the 12th. The Arquebus was 16th
Gauntlet: Dark Legacy on the consoles had a great system. They made monster classes unlockable where each class had its own animal version where just the model was changed. A demon class can be done. Would be like unlocking a skeleton model for the necro in Diablo 2. Does it have different moves? no, its just a different model. Using Diablo 2 monsters. A fallen shaman could be unlocked for the witchdoctor, the Bloodlord (duel weilding minotaur) could be for the Barbarian, Finger mage for the wizard. From a role playing point of view, players can use the human characters vs monster characters for their fantasy. If I programed the game, I'd bring back the horadric cube and as a secret level/quest, have to put a portal tome in it with a class specific weapon and armor to create a portal to the class specific level, where only a certain class character can enter. A alternate model for each difficulty level.