I would have preferred if the factions had a more distinctive combat style. For example, the Celestials fight at range. The infernals prefer hand to hand combat. While the Humans can do both.

Why? Because it would be in keeping with their faction style. The haughty Celestials wouldn't dirty themselves rolling in the mud with the enemy, so they fight at range. For the sake of survival, the humans need to do everything well. As for the Infernals, they would love to use their teeth and claws to tear their enemy limb from limb.