If anything, React is becoming less of a black box, with a 'simpler' API. It's just that in the process to moving to or learning the new API, people are understanding they didn't actually understand React before. They're now being made to confront that.
You can disagree with him fine, but I'm quite sure the founder of Formula knows what he's talking about when it comes to React.
I've only touched that package a few times since but it never fails to make me wish the original lead hadn't used Formik. I dunno, forms in react have never given me tears, but contrary to Formik's slogan it has been painful, even aside from this versioning fiasco, so I'm not sure this endorsement is as strong as you think it may be.
What I'm saying is silly is to say the author is somehow "uninformed" when it comes to React like he's some sort of newbie, as opposed to the guy who wrote the library that a sizable percentage of React apps use for their form components.
The author is Jared Palmer. He's a well-known engineer who has worked with React for years, and the author of a very popular OSS React library (Formik).
I used Formik long before hooks, then later, after hooks. I remember hesitating a few times because some of the exceedingly neat pattern/syntaxes were impacted negatively by hooks.
I still "happy" with both, but my team is all quite senior and I feel for jnr teams trying to grapple with React AND hooks at the same time.
In fact, it smells like the author doesn't know what he's talking about; in my experience "That will break for the following incredibly subtle reasons:" is usually about React fundamentals such as being deliberate with state mutations.
Custom hooks are some of the most useful and fun code to write, in my experience.