When people say "writing is thinking" what they're really talking about is not so much the "writing" or even "thinking" per se, but rather the "crystallizing your thoughts in to something concrete". Certainly my own thinking tends to be somewhat vague until I actually write it down, at which point I tend to get less sure of things because "oh, but what about this?" start to turn up, or I spot fallacies in my argument (the better reason to learn about fallacies is to spot them in your own arguments, not to bludgeon other people's arguments with).

In my experience writing is a very good way to do that, but if verbally works better for some then that's fine too.

In that sense I do agree with Graham that "I have some thoughts about X and I'll let ChatGPT take care of the details" is perhaps not entirely ideal.

All of this also applies to code by the way, in more or less the same way.