Not the OP, but our company Measured is building Puck as an open source project, so I'll try and answer.
Puck is targetted at content/CMS use cases, rather than general UI building. So the ability to establish guardrails in the editor experience is intentional. For best effect, we envisage Puck being used alongside a well-considered library of on-brand composable components. The aim is to enable non-developer editors/authors to freely update and build content, whilst keeping the UI consistent and on-brand.
This is a problem area we've encountered many times in our client work, hence why we wanted to scratch this itch.
Having said that, I do believe the Puck editor GUI _can_ be configured to work with remote data somewhat as you describe, using the adaptor linked above (but there's currently no demo for this feature).