If I had to summarize this I'd say don't fall victim to hype cycle and marketing. Make technical choices based on the problems.
I've worked on teams where CSS was a mysterious language with many gotchas. So I can see how Tailwind can help with this.
However, I wrote this article for the love of CSS, web standards, and the web in general. I think Tailwind's dishonest marketing tactics aren't doing good for the development community. Especially for young developers who are suddenly told that things like separation of concerns and good naming practises are a bad thing.
But in that instance, all of those css rules will still exist, but they’re stored in a separate css file and given a class name.
Having the reusability at the css class level means that someone else might break your component by updating the css.
With Tailwind, the reusability is at the component level. All the styles are self contained. No one can break your component accidentally.
He’s not saying “separation of concerns and good naming practices” are bad things, he’s saying that separation of concerns between HTML and CSS is mostly a false separation (it’s the same concern - making the UI look right) and that good naming practices are hard - best just do that in one place, the component that address the concern with both style and structure.