I see it similarly with the language models: The human provides the concepts and the "AI" formulates this, helps with structuring, etc.

That's how I am starting to see it, too. Another thing that occurred to me after posting is that AI writing styles are nearly certain to influence human writing styles. It's not a 1-way street. Even things that are written by humans may start to resemble AI texts.

Watermarking (i.e. white box techniques) is great for AI that wants to be recognized, but yeah with Open Source and private models, I can't imagine a way to make it universal. At some point, I think we'll just have to assume that everything we're reading was written or assisted by an LLM.

I haven't had any motivation in the last few days (I even switched on my PC today for the first time in several days) and now the sky is full of clouds.

I was counting on clear skies last night, but I didn't get them. Maybe tonight.