I don't understand this point specifically. I make all buttons on a site have the same theme without needing a framework, library or build-step!
Why is React (or any other framework) needed? I mean, you say specifically "React is also how you get consistent design across a major web app.", but that ain't true.
However, as you build more complex and interactive applications, you need "framework", like React. It's essential to simply handle the complexity of such applications. You will not find a major web app that is built with out a framework (or if it is, the owners will essentially have to create their own framework).
When you're using such tools, they are how you enforce consistent UI. Take Tailwind, the hugely popular CSS framework (I believe its #1). They have nothing to do with Javascript ... but even they willl tell you (https://v3.tailwindcss.com/docs/reusing-styles#extracting-co...):
"If you need to reuse some styles across multiple files, the best strategy is to create a component if you’re using a front-end framework like React, Svelte, or Vue ..."
The author is completely mistaken in thinking React ... or even that layer of web technology at all (the development layer) ... has anything to do with what he is complaining about. It has everything to do with design choices, which are almost completely separate from which framework a site picks.
A button should be styled independent of the framework. That's how you will get consistency. Same with every other non-component element.
The use of the component framework should be to consistently style non-primitive style elements (all the standard HTML elements).
What value is there in using React/whatever in styling buttons, links, paragraphs, headings, various inputs, etc? Today, in 2026, even menus, tabs, etc are done with nothing more than primitive elements; what value does React bring to the consistency of menus that you don't already have?
Speaking as a user not a developer, it'd be lovely.
Not a webdev, but can't you just use CSS on the <button> element for that?
There's a reason why 99.9% of web apps use JavaScript, and with it a tool (framework) like React, Astro, Angular, or Vue. And if you're using such tools, you use them (eg. you use React "components") to create a consistent UI across the site.
But again, which tool you use to develop a site has very little to do with what design choices you make. A React dev with no designer to guide him might pick the most popular date picker component for React, and have the React community influence design that way, but ... A) if everyone picks the most popular tool, it becomes more idiomatic (it's not doing this that creates divergence), and B) if there is a human designer, they can pick from 20+ date picker libraries AND they can ask the dev team to further customize them.
It's designers (or developers playing at being designers) that result in wacky new UI that's not idiomatic. It has (almost) nothing to do with React and that layer of tooling, and if anything those tools lead to more idiomatic design.
This Twitterism really bugs me.
You took the time to write a really detailed response (much appreciated, you convinced me). There’s no need to explicitly dunk on the OP. Though if you really want to be a little mean (a little bit is fair imo), I think it should be closer to level of creativity of the rest of your comment. Call them ignorant and say you can’t take them seriously or something. The twitterism wouldn’t really stand on its own as a comment.
Sorry for the nitpicky rant.
It bugs me that the author is "dunking on" React without knowledge on the matter (React is the tool you use to enforce consistent UI on a site; it has almost nothing at all to do with a design decision to have inconsistent UI). So I guess I "dunked on him" in response.
But ... too wrongs don't make a right. I'd remove the un-needed smarminess, if it wasn't already too late to edit.