I agree with a lot of it, except for this: "And someone who never writes has no fully formed ideas about anything nontrivial." I guess it depends your definitions of "nontrivial" and "fully formed idea". But consider all the experienced auto mechanics in the world. Few of them have written anything about it, but I'm sure I would judge most of them to have fully-formed ideas about a nontrivial topic. To generalize, I'm claiming that experience can give you fully-formed ideas whether you write or not (although writing will probably help).
> I'm not saying that writing is the best way to explore all ideas. If you have ideas about architecture, presumably the best way to explore them is to build actual buildings. What I'm saying is that however much you learn from exploring ideas in other ways, you'll still learn new things from writing about them.
