FWIW completely deleting numerous images might be quite laborious and slow. Maybe it is intentional so people do not very lightly delete and then regret doing so.
I just had a "good" chance (*) to test this when I had 39 000 images to delete. I first tried to delete them via Sequoia Photos.app but "Syncing..." remained on the Photos.app screen for hours even after an initial 100 image delete test.
Uploading all images took one day (500 Mbps down/up fibre) so maybe I was just too impatient updating such largish library (just cancelling iCloud Photos might have also removed them after 30 days especially when I reduced iCloud from 2 TB to 200 GB for just iCloud Drive which works OK).
Anyway, I then decided to test if deleting from the upstream iCloud source is faster and went to the iCloud web site and deleted Photos there. But it is possible to delete only in 1000 image batches and after each delete the user has to wait about 30-60 seconds for a "save". And the same happens also when completely deleting the images from "Recently Deleted" where also only 1000 batch is allowed and it also lasts about 30-60 seconds for each batch.
(*) p.s. I just tried iCloud Photos family sharing with those 450 GB 36 000 images and 3000 movies with 2 TB iCloud account. Long story short: IMHO user experience was not good so I reverted to the manual Finder sync to an 256 GB iPad although it can not hold that complete 450 GB Photos library so I have to sync only selected albums.