No, from a technical point we have to sync from Arch-Stable and then add our overlays. Sometimes we do a snap and remove blockers or we sync from Arch-Stable.
stable-staging is a repository only for us maintainers and developers. Testing gets regular updates when we have a set of packages ready.
Currently everybody is concentrating on Stable branch, as we published Gnome 3.36 there. So we only update Stable and Unstable branches. When we have a set of packages again, we will snap it over to Testing. So in short, if you use Testing you're helping us to test some packages, but it doesn't mean that we update as frequent as in Unstable or Stable branch.