I think we're really in agreement about everything. The tools have intended jobs; some people use them incorrectly or without regard to best-practices. Both have different strengths and failure modes.

I would say JSX and the separation of presentation / behavior is orthogonal.

JSX is just a Javascript powered embedded SGML-like document.

The combining of presentation and behavior is caused by render() being defined inline with implementation.

You can not use JSX by using ReactDOM directly or a templating library while still keeping render() inlined.

Or you can move render() to another class (or subclassed, or HOC, whatever) and separate the presentation and behavior with or without JSX.