how much diversity is there between "heroes"? is it just what weapons they use? because looking at the vikings, it just looks like: 1 big axe, medium axe and a shield, two small axes
unique hero special moves / traits (e.g.: conqueror can hold m2 to wind up his flail, and has better guarding than heroes like kensei), each hero has unique customization options, i
think different stats like health, different movesets and changes to standard attacks (e.g.: conqueror's light attacks aren't considered a combo but can be swung infinitely)
this is just all i can remember, but yeah tl;dr each hero plays a lot differently from the others in their faction, warlord (i think the viking with the shield) plays a lot more defensively and is better at getting a couple hits in and backing off compared to the berserker who works a lot better constantly being in their opponent's face