Responses
Yeah true, it's been long enough that it's easy to forget but from what I remember the readers at least are aware that Isidore is a powerful mage because he uses magic for his appearance and business as the information guild leader. Though in-universe its not disclosed to people and isidore's family is basically known for their money.
Wait... People don't know that Isidore is a powerful mage? It's just that what Deborah's father said is weird