"The spending condition is enforced by the mint." = trust me bro
if it were a worthwhile amount to steal, i just have to persuade you to sign on the message hash and done
This is a custodial solution. There is always a level of trust in a custodial system. This is an improvement to everyone using custodial WoS or Alby. If you want to maintain full custody run your own lightning node (and/or mint)