I view EH vs SD as a tactical choice.
SD basically amounts to impact hits on the charge, and helps you kill targets you need to shock down in one round. Its front loading your subfaction damage in bursts. We are already very VERY much concentrated on doing damage in our own charge phases, and you need to use this bonus damage where it matters most. We are already designed to basically win or lose in the charge phase thru debuffs and morale attrition, doing extra on the charge is hyperfocusing on this.
EH focuses your subfaction boost outside of the charge phase, and outside of positioning. It activates regardless of your and your opponents skill at screens, positioning, and combat. Best used for chip damage on targets you arent confident you can reach, shock dead in one go, or otherwise cannot handle and need softening.
Honestly I wish there had been a defensive subfaction choice, like restores d3 wounds of models for d3 units per turn, or reroll armor saves, lowering the WoT -1 to hit threshhold or awarding -1 to hit in addition to other WoT procs, or something, as we are already extremely dependant on our own charge phase.