It’s important to remember the Copyright Office guidance isn’t law. Their guidance reflects only the office’s interpretation based on its experience, it isn’t binding in the courts or other parties. Guidance from the office is not a substitute for legal advice, and it does not create any rights or obligations for anyone. They are the lowest rung on the ladder for deciding what law means.

The author suggests that a ruling that an AI can’t synthesize images from multiple sources might affect human artists who use multiple sources as inspiration. But those humans can look at 5 different paintings, create a 6th which is inspired by (but not identical to) the other 5, and get copyright protection for that, to protect their creative efforts. AI cannot, under current law. So when an AI combines five different paintings, who owns the copyright on it? The Monkey Selfie was ruled to be in the Public Domain. But AI can’t be treated similarly; It seems absurd that you can put art through an AI “copyright wash” and end up with something free of copyright.

You said it yourself in the first paragraph, humans using machines have always been the copyright holders of any qualifying work they create. AI works are human works. AI can’t be authors or hold copyright.