GmsCompatConfig v25+ this only get's updated with each OS update at the system level
This is incorrect.
GmsCompatConfig updates happen independently of OS updates, it's the whole point of GmsCompatConfig.
Version of GmsCompatConfig doesn't affect the visibility of Play services in Apps. If GmsCompatConfig is outdated, it'll be updated when Play services is being installed.
You're likely conflating GmsCompatConfig version with GmsCompat version. GmsCompat version can be updated only when the OS is updated. But even then, older OS versions will still have access to older versions of Play services that is supported by GmsCompat version that they have. For how long is not decided yet, we can't keep old versions of Play services in Apps repo indefinitely.
Currently, Play services is hidden only for those users who are running GrapheneOS version older than 2022120600, which is the last time GmsCompat version was incremented.
This version is 6 weeks old at this point.
Legacy version of GrapheneOS that is based on Android 12.1 (for 3rd gen Pixels) was updated to the latest GmsCompat version more recently, at the end of December.