I wish you were right, but this is unfortunately wrong – and it's not because developers don't know CSS well enough, but rather that CSS is just plain not good enough. And ridiculous new features keep being added to it when we still don't even have some of the necessary primitives that should be there.

As an example, one of the most basic components I can think of is an accordion. You simply can't make one that works in a visually pleasing way (the way most people would expect!) in CSS because you can't animate to or from `height: auto`. The best you can do is some cop-out technique of fading out or squishing the content with `transform` and then having the content that follows it do an immediate jump up/down.

Instead, animating an accordion that actually animates the layout around it smoothly absolutely does require JavaScript, to tell CSS what non-auto values it needs to animate to and from.

And that's just the most basic component I can think of!

Another example: anchoring one element to another, when those elements don't have a parent-child relationship. Think tooltips. This requires JavaScript to measure the anchor element's position on every goddamn frame and keep the other one in sync, when the layout engine already has all the necessary information and could easily be built into CSS.