Reason? Earth has 5s internal CD and works only on single target.
Strength has no internal CD, with rabid amulet you crit a lot, you do a lot of aoe and you get 3+ stacks of might easily. So 35-105 power/condi dmg easily. More, most of your attacks are AoE in some form so due to that you quickly catch up and exceed dmg lost by switching earth. Throw in the fact that confusion and burn get huge boost from it and it's kinda obvious Strength > Earth.
Play with it and love it. Strength + corruption on p/p is kinda sweet
EDIT: As of 14th Dec this is no longer viable. SoS got ninja nerf and received 10s Internal CD. Before it had none. That and the fact that on weap swap sigils are now viable!
EDIT 2 One of my personal favorites is now Superior Battle. 9 stacks of might doable without any traits or +boon dur really. Geomancy and Hydromancy are also great especially for condi/bomb kit specs. Combined with enhanced performance and HGH 20+ stacks are easy to keep up.
Edited by Killyox, 15 December 2012 - 12:45 PM.