I was comparing these two chain lightnings by efficiency. On a lightning based Warder, Chain Lightning from Seal of Skies dealt an average damage of 10k per crit (not a level 100 character, still leveling) and Aether Lightning from Arcane Tempest dealt average of 6.5k per crit.
To compare those, The Arcane Tempest has stats of:
And Seal of Skies:
The problem kind of lies in the damage, since Chain Lightning (CL) has more base damage and WD. The only advantage of Aether Lightning (AL) is 7 targets max instead of 3, as in CL. Seal of Skies is very easy to get, since you just craft it whenever you want and put it to your weapon, while AL needs to be farmed. My idea is to increase the damage of AL or completely remove the hit cap. Examples:
75 Energy cost
Affects all targets
45% Weapon damage
105 - 340 lightning damage
240 aether damage
+35% crit damage
or
75 Energy cost
Affects up to 7 targets
55% Weapon damage
190 - 340 lightning damage
100 - 320 aether damage
+35% crit damage
NOTE: The Arcane Tempest’s Aether Lightning should be way stronger because you obtain it by collecting a full set and it takes 3 places from your inventory, while Seal of Skies buffs your physical damage to lightning and takes only one place in your weapon enchantment slot.
I chose to set the aether damage to a random value because buffing it straight up to 320 while also buffing the lightning damage could be a bit too strong. You can still change both damages in both Lightnings to aether/physical (for AL/CL respectively) using elemental -> aether/physical conversion from items, and then CL will still have a better score because it’d be 100% physical and AL would still have 24 - 36% lightning damage due to its own conversion (not a problem in certain builds where you can reach over 1700% elemental damage and around 3000 aether damage).
Summarizing, AL is too weak in comparison to CL and I think the best way of buffing it would be the first example I wrote where you remove the target cap, since straight up buffing damage could have its downsides if we talk about being too stron. In certain builds, where an Arcanist with elemental conversion or massive elemental and aether damage would annihilate everything by only holding one button.