While whirlwind is no Black Tome or Cats Claw, it's still a bit of a booby prize to be rewarded with when crowned. Of the 3 artifact missile weapons it has the lowest stats and has the worst ammo available for it. I propose it's made a giant slayer (giants, cyclopses, titans etc) to make it a little bit better, citing the story of David vs Goliath for thematic reasoning. Waddaya think?

Edit: should say, I don't think this would make it overpowered as the much better bow has undead-slaying powers, and access to much better ammo. Unless slings become massively more powerful than bows and crossbows at higher skill levels and I've missed it...