I'm a WordPress developer at an agency that designs and develops custom WordPress sites for B2B clients. FSE and to a lesser extent Gutenberg are useless to us. Our clients hire us to design and develop a custom website, they obviously don't want to have to worry about the design themselves. WordPress used to be a simple CMS that could handle content management on the backend and we as an agency could handle design on the frontend via our custom theme. Our clients don't want to mess around with design, they just want to be able to easily update content and add pictures. We've used ACF for years to customize the backend to easily facilitate this but FSE and Gutenberg just over complicate the whole thing. WordPress doesn't need to be overly complicated and turn into another Wix or Squarespace.