I don't understand your point, to be honest. A lot of language features are just syntactic sugar for lower-level language functionality. ES6 getter/setters are just syntactic sugar for Object.defineProperty. Does this mean that ES6 and ES5 are the "same"?
No, of course not, but ES6 getter/setters are specified in ECMA-262 and JSX is not, so ES6 gets to be called JavaScript and JSX doesn't. It's really as simple as that.
My point is that because JSX is not JavaScript it then requires a ton of complexity to use it. Whether that complexity is justified is up to each person, but we can't ignore that complexity exists when arguing it vs. alternatives.