Right, you need to be knowledgeable enough to delegate. It's genuinely a tall order to be able to figure who is a good product leader, who is a good CTO, who is a good CFO, who is a good litigator, head of HR, etc. Those fields are so disparate, and if you don't know enough about them, you won't be able to judge talent.
It's exactly the same reason that programmers need to be interviewed by programmers, and programmers prefer to work for managers that were programmers. You really do have to understand something about someone's job if you will manage them (and potentially fire them).
People with specialized knowledge will do all sorts of things to mislead you about their job performance -- doesn't matter if it's an engineer, lawyer, or finance person.