Floorp is still Firefox at its core as it’s still using Firefox’s UI and building on top of it, while Chromium can be embedded into a GUI (see Vivaldi and projects like CEF and Electron). That doesn’t discredit it, in fact some of Floorp’s changes are pretty good for customisabiity and user experience. That being said, I was told that the engine powering Firefox was able to be embedded but it had many issues to the point where integrating Chromium was easier.

On a similar note, I know Pulse Browser is part of an overarching project to make forking of Firefox an easier job, and I know they and the Floorp people are friendly.