Mobs out in the open world generally have higher movement speed and higher attack speed than you. If you were to stand still and trade hits with a mob back and forth you may end up trading 1 of your Auto attacks for 2+ of theirs. If executed properly, The Hamstring Method allows you to trade 1 hit for 1 hit with a target, drastically reducing your damage taken while not reducing your damage at all since you are monitoring your natural auto attacks with the swing timer.
Travel Time is what you will be doing the most of, thus talents or abilities that increase movement speed will likely have the highest impact on leveling speed.The more important concept is this: Shaving off seconds of downtime between pulls is equally valuable to shaving off seconds of In Combat Time. When you think about it this way, Damage Mitigation and Regenerative talents / abilities / stats have almost offensive properties and should potentially be valued equally to stats that increase damage.