The elemental mod is used because the Grasping Darknesses have 40AL more against physical damage than elemental damage. It'll speed the run up, if only marginally. There are no key synergies dependent on damage type. Similarly, you could switch to sundering for the smites, though I suspect the difference will be negligible.
The exact positioning of the Darkness pull doesn't really matter. The key is that using Sprint will allow you to break off easily from the Aatxes, but the Darknesses will still follow because they have an inherent 50% speed boost. You just need to move around so you aggro all of the Darknesses and don't get trapped. You can survive a hit or two from the Aaxtes but obviously it's better to avoid them.
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