Yes, it's Aether vs Aether. This is from the pattern of Fire's weak HP vs Fire Shield and Gravity's heavy HP vs Weight. Sometimes the best counter is in the same element.
This shield would do well to counter immortalized heavy hitters -- particularly dragons and growers (blasted irritating #@% @#@#% immortal spirits and lava destroyers). While yes, Fire Shield/Buckler can be used against them, they shouldn't be the only real option. imho of course ;-)