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Unless you're Steel/Dragon (RIP Archaludon) or Fairy/Dragon (RIP Mega Altaria) you're always weak to Dragon LOL. That's like saying Dragapult is weak to Dragon so it shouldn't rise
Not every Pokémon dominates the meta even with Tera Blast. The existence of "Tera Hogs" means that Tera Blast isn't the issue and it's just Volcarona. I'd support a Volcarona test but not Tera Blast