To me, 'sophisticated' connotes complexity in a way that means I'd never use it to describe something extremely simple or minimal, including Hemingway's prose— even if it meets the definition of another sense of the word. I might use other adjectives to praise it, but not 'sophisticated'.

And I think any reasonable curriculum should include some 'sophisticated' texts in the narrower sense described above. I actually don't think that sophistication in the sense of worldliness is as important a thing to try to ensure in this kind of curriculum. That's more a matter of fashion or ingroup signaling than any textual feature, and you'll get it for free in any school curriculum anyway— preexisting canons will impose themselves one way or another and demonstrating fluency in the canon is the main thing that evinces sophistication (divorced from complexity) in a text (or a student, for that matter).

I agree with the rest of what you're saying, though.