Earlier quoted context omitted.
Could you paste the simple script tag that makes React work without transpilation? I always thought you needed Webpack (or an equivalent) to transpile JSX into a vanilla js function the browser can interpret. If you're referring to Create React App, it uses Webpack - just preconfigured so you don't have to fiddle with it before you start building.
In the docs: https://reactjs.org/docs/react-without-jsx.html Unfortunately it uses ES6 features. There's no ES3/ES5 demo without JSX -- https://reactjs.org/docs/react-without-es6.html uses JSX
As an aside, is that really a problem these days? All modern browsers now offer comprehensive native ES6 support. Unless you still need to support older platforms like IE or some of the legacy mobile browsers, it's mostly a non-issue.