

They're stronger, yes, but strength is already an advantage in combat. You've just taken a group of thugs and given them leather armor skin and steroids. The tech level is a general medieval fantasy era, though a very primitive sort of gunpowder is present, similar to the one found in medieval China. With equivalent intellect to humans, would a race of humans like these have developed different tendencies in warfare, both amongst each other and against common humans? With those clear physical advantages, would this group be able to take a typically 'barbarian' fighting style, counting on their toughened skin to supplant for more common armor? Culturally, they would also have incentives to do so to have body tattoos that they value in display, though they do wear armor if they feel they have to. In addition to that, they also have a skin that effectively serves to be as effective as regular leather armor. I've got a variation of 'humans' who have superior strength on average, with the top fourth of their population being comparable to 'The Mountain' from "A Song of Ice and Fire" (Roughly 8' tall and capable of killing a horse with a single punch).
