"React is, in my opinion, the premier way to build big, fast Web apps with JavaScript."
Nowhere in the documentation does it stress that it's easy to learn or ideal for beginners. If you don't know Javascript, writing React applications (or any application, really) is going to be painful. Full stop. JSX adds cognitive load when writing code, but reduces cognitive load when comparing the DOM to the component that created it. Given the amount of time I spent debugging and refactoring, I'm happy to use JSX.
Maybe it's the article's title that has understandably rankled some people by seemingly maligning JSX. However, I think it's a very valid concern to have when ramping up a team that's unfamiliar with JS and React.
I'm not in the situation of ramping up a team unfamiliar as the author was. But it sounds like he was experienced with JS and React himself. Or are you suggesting he should replace his team with people more familiar with JS+React?