Every DE is designed to be used in a distribution. I think what you are trying to say is that GNOME is designed to be "finished" by the distribution, which is a completely made up idea. Show me where GNOME says you need to finish the DE yourself during integration. GNOME is designed as a complete DE, the reason Canonical/System76 change it is because it's poorly designed for new users/casuals, which is their user base.