Fantastic summary of Gutenberg’s mistakes. They also completely missed the Headless CMS movement when they designed Gutenberg this way.
Having said all of that, we use Headless WordPress for many many client projects and have got it working really well for us. For us it’s much better than Sanity, Craft and Prismic. The WP-GQL plugin and ACF are really amazing.
Nice, that's good to hear! I've been using Contentful which has felt super familiar to editors and devs alike, but does have some pain points, such as the lack of ACF-like repeaters (IMO the relationship fields don't stack up as well for what we normally do for clients), the never-ending modal rabbit holes you go down to edit nested content (page -> section -> component -> image wrapper -> image, all because you can't force alt text on their default media uploads, and that was their suggested method of getting around it!).
Having said all of that, we use Headless WordPress for many many client projects and have got it working really well for us. For us it’s much better than Sanity, Craft and Prismic. The WP-GQL plugin and ACF are really amazing.