Perhaps the first difference between us is I immediately assumed PG is talking about transmitting ideas (argumentation or proposition), ie writing essays and not writing fiction.
What I assume he means about “writing not being pure ideas”, he means there’s an overhead in transmitting ideas via writing. This is analogous to using programming languages to capture ideas, hence anything but simplicity offends because it is analogous to (in)elegance in code.
I think this essay is excellent but it seems I was more attuned to his message, or at least it met my expectations.