To that point, given a corpus of writing from person A and another from person B, I have no doubt it’s easy to train a classifier to determine who wrote what. In fact I believe law enforcement agencies already have these classifiers.
The only difference here is that Anthropic is actively trying to make the watermark undetectable.
They're not trying to make the watermark undetectable, that would defeat the point of a watermark. They're making it detectable, but not make the text obviously watermarked
Undetectable by a human reader. Come on, give the post a charitable reading.