In Unity, the enemies had life chunks on their bar, as they do in Syndicate, but in Unity your damage was very dependent on the weapon you used and your damage stat. Positioning was important in that enemies didn't have to wait for one another. You could be surrounded and killed. But, as with all previous AC games, the engagements were locked into animation.
In Origins, they completely opened it up so combat depends entirely on hitboxes. Level and loot makes an huge difference.