We use the User Configuration/Preferences/Control Panel Settings for deploying printers and with using the FQDN of the print server (server.domain.edu) and have no issues with hundreds of printers GPPs and targeting groups, as others said you do need loopback processing if you are applying the GP to the computer not the user objects in AD. For the default printer that might be the Let Windows Manage Default Printer.
GPP
User Configuration\Administrative Templates\Control Panel\Printers\Turn off Windows default printer management
Registry Key
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Windows
LegacyDefaultPrinterMode
D-Word Value = 0
https://www.tenforums.com/tutorials/26138-turn-off-let-windows-10-manage-default-printer.html
https://answers.microsoft.com/en-us/windows/forum/windows_10-other_settings-winpc/group-policy-disable-let-windows-manage-my-default/789ff603-67a8-4247-bedf-bf5a6ea327a5