The GPS constellation is considerably more robust to a ground station outage. If the ground station goes out, the satellites themselves are a distributed network and they use each others' data to correct themselves. It can operate in this mode for something like 60 days before it's unable to continue correcting itself.
Of course, if the ground station failure was a soft failure, and instead of ceasing to upload, it began uploading incorrect data, the GPS location results would be arbitrarily bad to unusable. It's not clear to me whether the Galileo outage was because of a hard ground station failure or a soft one. But given that one of the contributing factors was that the backup system was not online, it would indicate to me that this was a hard failure that GPS would have been able to correct.
The other factor for the US GPS system is that there are actually over 24 ground stations, one for each time zone plus at least a couple of spares. A local failure in one time zone doesn’t take out the whole fleet — they can fall over to a backup ground station, and backups for the backups, etc....
Of course, if the ground station failure was a soft failure, and instead of ceasing to upload, it began uploading incorrect data, the GPS location results would be arbitrarily bad to unusable. It's not clear to me whether the Galileo outage was because of a hard ground station failure or a soft one. But given that one of the contributing factors was that the backup system was not online, it would indicate to me that this was a hard failure that GPS would have been able to correct.