The issue is, if I’m using JS, why on earth would I ever use PHP? I can just await file('index.html') or return <IndexPage>

The cognitive load is null. You’re just having trouble breaking apart your learned behavior. Returning a component of jsx is just the same as writing an include for PHP.

So if returning a component is the same, how would one (PHP) be more painting oneself into the corner than the other (JS)?