Yeah I'm not putting scarf on Ttar. It's fine as a one time thing, but if I'm aiming to get to the semifinals, etc. scarf is not the way to go.
I don't like Garchomp though, haha. Never used one, probably never will. Nothing wrong with it, but I just don't like it. Well, it's also not a counter to Volcarona. After a little bit of damage (let's say a fake out), Volcarona can OHKO Garchomp with Bug Gem Bug Buzz. It does resist fire and is neutral to bug and outspeeds Volcarona, but if opponent leads with Fake Out + Quiver Dance and I don't have Chandelure out, something my team's fainting on the 2nd or 3rd turn.
... One of the reasons why Crobat is good, haha. Outspeeds and OHKOs Volcarona, immune to fake out, OHKOs plenty of rage powder pokemon (for those that do Rage Powder + Quiver Dance), 4x bug resist means Volcarona either dies on the turn it attacks (if it gets a QD and outspeeds Crobat) or it forces Volcarona to use its fire move (making Volcarona easily predictable).