An example:
Application Payload = 100MB AppImage all inclusive image with deps = 175MB Flatpak App Layer = 101MB Flatpak Deps = 75MB
Now say you're shipping 1000's of similar applications with the same general dependency chains in bulk operations to things like end-user devices.
Flatpak wins. That's the point.
This isn't a discussion about an average Desktop user saving some disk space.