None of the Uniques or Legendary aspects actually boost the damage of Lightning Storm. Earth has +2 ranks when you have any Fortify, plus constantly generating Fortify makes that a pretty reliable strategy. Werebear and Werewolf, +2 ranks while Hurricane is active, not to mention Mad Wolf and Insatiable for just +2 always, plus each of the Key Passives are like “oh yeah also do 30% increased damage”. Hurricane even has that one that’s +15% damage each second. But Lightning Storm? All the lightning-related powers like Runeworker’s, Overcharged, and Lightning Dancer’s, as well as almost all the lightning-related Passives, are focused on triggering these bonus lightning hits for flat damage, but those hits can’t Lucky Hit, they can’t trigger anything in any of the three Nature Magic Key Passives, and they don’t scale with Lightning Storm itself, so they’re not actually all that useful for anything other than clearing trash.
I’m finding I’m capping out around Nightmare Tier 60, and I’m starting to realize there isn’t actually anything out there that can get me any further while my build is still centered around Lightning Storm. I wish I could just like try an Earth-focused build, to see whether that actually gets me any further (or it ends up turning out that the problem is me), but the Lightning Paragon Board is the first one attached to my starter board, so replacing that means undoing ALL of my Paragon points, not to mention that almost ALL of my gear has something Lightning-related on it, so I can’t really just “try a different build” at this point. Am I bricked?
I am literally in the same boat as you on my druid. Sad thing is that Lightning Storm is actually one of the most fun and visually appealing spells to use in the game. Shame that it will be relegated to collect dust in the talent tree.