My points proved conclusively that coordinators are trustless. You can even use all 3 anti Sybil methods together at once, you don't have to rely on just one:

- First, register your private coin to the coordinator. If it's accepted, then there's no Sybil attack.
- Second, ask your friend to register a coin to the same round. If it's accepted, then you've confirmed for a second time that there's no Sybil attack.
- Third, just to be absolutely sure, back out of the round during signing to check to see if the transaction was built to target you. If the transaction is created, you've confirmed for a third time that there's no Sybil attack.