It's not so much that churn has been greatly reduced, but that the worst churn has started to be centralised and hidden behind tools like `create-react-app`.
There will still be more churn as people come up with ways to be more productive, however it will be hopefully concentrated in areas other than build process tooling.
You're spinning this as a positive thing, but the fact that a UI library needs its own build tool does not speak well to the state of front-end development.
Specifically the fact that we still don't have modules or widely-deployed http2 is what makes the build tool complexity necessary.
I wouldn't say that was spin, I said that build complexity is likely going to be handled by fewer engineers. The underlying problem still exists but less people need to put their oar in: that's bittersweet.
You're pointing to create-react-app as a solution to JS churn when it was just created 2 and a half months ago.
The fact that people keep thinking that a 2 and a half month old project is the solution to all of their web development problems is exactly why there's so much churn.
Every new tool overtakes the previous generation by being superficially more simple, only to add complexity of its own over time until the next generation repeats the cycle. It turns out the complexity is there whether you acknowledge it or not, and over time your leaky abstractions will burst.
I don't think that will happen with create-react-app since its intention is zero customisation.
You can't generate more complexity with a tool that reduces opportunity for developer choice.
A basic example is that a starter app would normally require you to connect 10s of libraries together just to get started. It is difficult to argue that not having to do so is actually more complex.
I remember building Windows ui apps 10-15 years ago, and that definitely needed a build tool. Http2 might be great for module loading, so things don't have to be bundled, but there's lots of unsupported use cases right? Css encapsulation, autoprefixing, hot reloading for dev, compiling features not yet in browsers into js versions supporters by browsers etc.
There will still be more churn as people come up with ways to be more productive, however it will be hopefully concentrated in areas other than build process tooling.