Fizberry wrote:
...but most of the photos are ones I never put into a folder to save.
This may be a misunderstanding. Imported photos are automatically saved in your Photos Library, whether you add them to an album or not. Albums are not storing photos. They are just grouping related photos by referencing them in the library. You only need to add photos to albums, if you want to organise them and keep related photos in one place for easy access.
if you want to delete thousands of redundant photos, I would delete them in small groups. Do not move more than thousand photos to Recently Deleted. You may not be able to empty the Recently Deleted Album, it is is too full. Add small numbers of photos to Recently Deleted, check them, if there is an important photo among them, that you want to keep, then empty Recently Deleted, before you trash more photos.
To prevent yourself from deleting important photos you could refine the smart album suggested by Fox Fifth and add an additional rule: Photo > Is Not > Favourite
Combine the two rules "Match All".