Template syncing to objects within a set and/or mass relation apply to all objects in a category/set. Similarly to Notion, or how master pages work in Indesign.
Allow templates to be synced in all affected pages through the types interface.
Very often users create a template and decide later that they need more relations added to it. This would enable this to be done quickly without having to manually go into each page and add or remove relations manually.
You could just do this automatically and allow users to disable it for individual pages. I think there’s more precedent for this way of doing things than how it is currently implemented. Most other programs like Figma and Indesign operate like this already.