There’s a 3rd option, but would require some scripting to Sonarr/Radarr:
You set that up on your Plex server and then configure Sonarr to hit the server on a specific port listened by plex autoscan to scan specific folders.
This would require uploading via
rclone move each new file to your GDrive and then having Sonarr hit autoscan endpoint to force plex to scan only the folder the file was just added to.
Or wait until the reading of the google change log comes in or go back to Plexdrive and come back later