There's no signing power. A ring signature is just a signature made with a set of public keys for one of which you know the corresponding private key.
Zero-knowledge proofs/cryptographic accumulators are used to verify each coin is spent at most once. Any of 11 coins could have been spent, each owned by a different single key.
For some reason, I thought Monero was basically ZCash plus using ring signatures to make traffic analysis much more difficult even if the zk proof system were broken. I was completely mistaken.
Edit 2: Sorry droffel, I wasn't fast enough editing away my old understanding of how it worked and asking what I was missing. Thanks for the explanation.