You plan the piece in your head, then write it out — and it comes out flat.
But that order is exactly the one job AI already does better than you: assembling what you already know.
The experts William studies do the opposite: they write to find out what they think, then rebuild the mess for a reader whose route was never theirs.
So is thinking on paper the part a machine can't take?
Yes — the thinking is the part that can't be automated.
Draft to discover rather than deliver, use a reverse outline to find the structure you actually built, then convert that private draft for the reader — clearing the interference between your thinking and their reading, in the words their world already trusts.
What the machine can't do is have something to say; writing to think is how you get it.