Doesn't make sense that any kind of aquatic terrain doesn't give Lighting +2 to enemies inside that zone, although they had a similar problem dealing with Burn tokens and water terrain.
The Lightning affinity traits make no sense whatsoever anyway. Even if we ignore Faraday cage effects, things like Wall of Steel should be Lightning Immune, not +2, and probably Iron Golem too.
But yes, Aquatic out to give +2 to living non-flying creatures in the zone.
Furthermore lightening always moves on the easiest path. To control lightning and direct it any way you want without a circuit should also be impossible. I would just pretend that a lightening attack is actually a missile or bullet made of magic, and the magic is fueling the electricity. Or maybe harshforge is weak to electricity, and most metals and earth have traces of harshforge in it. Maybe their version of steel is actually a harshforge-steel alloy. It would explain why the ground in Etheria isn't wildly more unstable then the ground on earth, even though Etheria has the kind of magic that you would expect to have warping effects on the environment. I imagine that the Grand Arena floor has a lot of harshforge underneath it, so that while people can cast enchantments and stuff on the cobblestone surface as well as on the dirt underneath that, the harshforge underneath the dirt keeps the arena floor from being ruined beyond repair. They just have to "repave" the harshforge with a new layer of dirt and cobblestone every now and then.
Of course this would probably make thunderstorms in Etheria be very different than on Earth. It means that in Etheria, either lightning strikes would happen in the opposite direction (from the ground to the sky) or that lightning is positively charged, or more likely, that lightning in thunderstorms are also fueled by magic. In other words the gods control the weather, or at least power it.
So, to summarize, if steel in Etheria is weak to electricity instead of resistant or immune, then one possibility is that harshforge is weak to electricity and that Etherian "steel" is actually a steel-harshforge alloy. If so, then it follows that Etheria must have weather gods. Or maybe there's something weirder going on...like some unconscious remnant of the Elemental Lord of Air is controlling thunderstorms. That would explain why things that get struck by lightning don't seem to have been intentionally or consciously targeted, but also why lightning strikes still go in the same direction as on earth despite their steel and earth being weak to electricity.
Or maybe it's something else entirely. It could be that lightning bolts in Etheria are generated by some other material than just pure magic. Maybe magically-charged and condensed air? If you condense air enough the water in it might start to get really cold. Maybe lightning bolts have tiny magically charged pieces of ice in them. The magic continuously generates the ice and sustains the electricity, and that ice absorbs mana from the surrounding environment and then shatters from the build up of heat, releasing more magic in a feedback loop. Of course it would make more sense if instead of ice, it was the same material that mana crystals were made of, and lightning bolts formed from magically charged, condensed and *dehydrated* air.