Etherion is the supreme magic, one that requires a lot of charging, a lot of MP and can only be cast by large organizations like the Mahō Hyōgiin or Mavis (who happens to be an unlimited source of magic). I strongly believe that Wahl's etherion is similar or slightly more powerful than Jupiter, but I don't believe Wahl is country level... The only country level Spriggan shown so far is Irene and even she hasn't been shown to have country level DC, just a country level spell.
No city buster, otherwise it'd have eliminated Magnolia, wouldn't it? Large building level or city block at most. No way that canon even reaches town level...
If Wahl's etherion happened to be the etherion, then not only would it be a suicidal attack, but since it'd pretty much nuke the whole Fiore, it'd kill most Spriggans too.