HTML CSS and JavaScript are just a small subset of web development.

And yes understanding them is still relevant. But when I started I was spending more time memorizing the the quirks of IE6 than I was learning how JavaScript, CSS, and HTML come together.

I think it you start directly in react you don’t learn the layer below it sure. But there’s no reason you have to start leaning react. There’s nothing inherent about starting today that forces you to start directly with React. You could start building a static webpage. And if you did that it would be easier and more fundamental than if you did that same thing 20 years ago because you can ignore most of the non-standard browser quirks.