From a "content as a page" perspective, this post rings true. From a "content as a data source" perspective, a fields API would be useful. Gutenberg dumps all of its data to html code, so individual bits can't be stripped out and made accessible to a REST API call. You can't get a value of 'single block' within GB content.

Where I work, we use WP as a CMS foundation for both Web and Apps. This means Gutenberg can be useful for managing web content, but you still need fields for specific application data, because specific data and types need to be consumed.

ACF fills this need just fine, and easily integrates with the REST API, so no major complaints from me. It just feels like WP is disregarding users who want to use the platform as an advanced CMS in addition to creating a website.

Last I checked, I am not wrong here, but please correct me if I am :)