There never was any separation of concern. Just because the HTML, JS and CSS were in different files don't mean they were truly separated. React embraces this fact and it's extremely refreshing. Each component's HTML, JS and CSS belong together.

> logic buried in HTML that is hard to find and hard to reason about

That's a complete non-issue with React and much more an issue of the traditional way of breaking it up in different files which look separated but in reality are extremely entangled.