Well, to be honest, iOS 11 was announced and available for beta testing and development in June. By following the safe area rules they could've started updating Gmail back then already. Then, the iPhone X got announced in September and they could've tested it in Xcode simulator from that date onwards. So actually Google had months the time to update their app.
Not saying we have the right to complain about a free app, but I personally used Gmail and Google Maps a lot less because of the app not being updated. I can't imagine Google wants users to use their most important apps less (I even tried out Apple Maps for a day, but ran back to Google Maps quickly enough). But both have been updated, so everybody can move along now