Through curation rewards, you gain additional leverage,

Once again, the definition of a sibyl attack is where you gain additional leverage by using more than one account than you would have had if you just used one account.

Curation rewards are exactly the same when voting with multiple accounts, and so is the amount you reward you give or take away.

Also, a sibyl attack is something thats made against the platform, not an individual user.

You really really don't understand the concepts youre trying to address.