Seems to me “people as His writing instruments” is sufficient to reject inerrancy. The point is that the Bible accomplishes His purpose perfectly while denying that it is perfect in any other way irrelevant to that purpose. It refutes the notion of “true if interpreted correctly” to uphold instead that nobody should think they can do better – a more reasonable understanding of Sola Scriptura.
I was tempted to say God as author is the higher view of scripture than auctor, and I thought that curious considering you gave scripture a higher score in this thread. But I think it is more complicated than this. In a literal treatment of both metaphors, the author sounds like he has the greater control. But I didn’t understand it in this way because unlike pens, people are alive and make their own choice, and I don’t think God controls them like a tool, especially in doing good (when I think people are more free). This is probably why you like auctor better since this an analogy using people rather than an inanimate object.