No, you are right. Flutter isn't really native since it uses Skia to render native platform look-alike components (as opposed to react-native which really use the platform)
As I’d guess most people spend most of their time in Chromium browsers and electron apps probably a case to make that ‘native’ in the sense you imply is Chromium!
This article is wrong about React: it does not generates unreadable CSS class names. CSS in JS libraries do.
By default, using only react + react-dom, you can achieve the exact same output as "handwritten HTML + CSS".
But CSS in JS is not bad either: it generates unique class names by using murmurhash on rules and it makes a lot of sense in a component approach (you can see it like an automatic BEM method).
Even better: The main pain point of this approach (runtime cost) will soon entirely disappear. Linaria already provides a solution, Facebook will soon roll is own (called StyleX for now). It will create a stylesheet file with atomic CSS rules (one rule per class) and replace the classNames directly at compilation time, offering deduplication, eliminates of dead code and maintenability without sacrificing performances. IMHO a huge step in CSS development.
Remix has 21,375 downloads per week according to npm. Next has 6,562,587.