Gutenberg isn't a thing for the folks I work with, nobody there likes freedom (freedom only leads to errors!), everything is form-based (ACF is slow but it works, and here, too, it's not users setting up the fields, it's developers) with a few shortcodes to pull in special elements.
I'm not complaining, I like building tools and solving problems and using WP allows for plenty of both, but in hindsight WP is slowing us down, I believe. Of course, it's hard to predict the scale of things when you start, so having something you can quickly iterate with is useful.
It's not to say there aren't some that say sod it and have their own UI library. But quite a few leverage wordpress admin styles and conventions (such as the wp_list_table).
But the quality is all over the place, much like with composer packages.