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This is a complaint I've heard often about React, and usually it's by someone that's never actually tried it (myself included before I first used it). But it's a visceral response. Until you sit down and give it a go, it's hard to believe that we had the separation of concerns wrong.We didn't. And React doesn't change that either. React components are not logic code, they are UI code, and that has always went with view concerns (loop this times, show this button or that button depending on state, etc).
In the Desktop GUI space, where they don't have our HTML madness, do you think their UI components are not using code? Buttons, drop-downs, etc are not appearing by magic, they are created by code that does things like: draw a line of x length and y color, then another perpendicular to that, etc, then loop and draw some stripes, etc. That's the case even in Smalltalk, where MVC was invented. That still matches with "separation of concerns" -- which is about not mixing your BUSINESS logic with your UI code, not about not having code in your UI rendering.
In fact, compared to the classical way (foreach and other kinds of template instructions embedded in template strings, from PHP's Twig to Angular) it's even cleaner, because even though JSX looks like HTML it's actually compiled to Javascript instructions it's not just some ad-hoc language hidden in template tags to be interpreted at runtime.
And separation of concerns also applies to UI elements (encapsulation, re-use, etc) something which "logic free" templates like Mustache and so also miss (or, well, make harder -- of course if you try hard enough you can always fit a square peg in a round hole).