you basically disagree with the default for DND also including unknown repeat callers (15min window). This is sensible, but sounds like an AOSP default trickling through.
The defaults are set via a default_zen_mode_config.xml at core/res/res/xml/default_zen_mode_config.xml · v1-q · e / os / android_frameworks_base · GitLab (and read out in core/java/android/service/notification/ZenModeConfig.java · v1-q · e / os / android_frameworks_base · GitLab) if you want to go for a pull request. You’d want to set repeatCallers="true" to false.
btw, what happened to the filed bug in Don't disturb mode and shutdown → was this resolved in Q for your device?
I see you’re involved where DND is touched, this seems user friendly: Decline calls if “do not disturb” is enabled (#1691) · Issues · e / Backlog · GitLab