VS is not ideal as a carry, but she can fill the role adequately. I wouldn't select her as the only carry for a team but she performs just fine as a semi-carry and can be a hard carry even if she's not ideal for it.
She gets a free +36% damage aura, she has an armor pierce skill with greater than 100% uptime, and one of the better stuns in the game. Her ultimate can be used as initiation, escape, and anything in between. She can fill the role of carry just fine; how many hard carries have a spammable stormbolt or an aura that boost their entire team's damage?
This is the entire point - no one's saying VS is a better carry than Anti-Mage or Morphling, just that she can be played as a carry and is effective as one. You might want to dial the attitude back next time if you want your stay here to be a happy one.