That 1 extra damage that lightning has over shockwave is very significant. Doing a quick count I came up with 8 unupgraded creatures that start with exactly 5HP. However I don't think the problem is with lightning but rather that shockwave could use another slight buff. It is worth noting that two recent cards (catapult, overdrive) have made creatures with high HP more viable. If this trend continues than the insta-kill effect will be worth having and the cards will even out on their own. Anyways, my point is lightning is fine, no nerf needed.
