Templates are horribly limited compared to the free mixing of js and markup Jsx gives you

If you use them raw, yes. They are just the building block you can build upon. And that's a really good building block. You can create your own parsers. I am doing exactly this for a framework that has yet to be released, full disclosure. Makes html clearly html, and javascript fully javascript. No bastardization of either one into a chimera. And the junction of the two is why the custom parser is required. But it is really light from a dev experience.