Nice find.
Could you check if the option "empty trash securely" in Finder preferences changes something?
According to experience, after enabling it, deleting contents will take much longer time if you delete many files or large files (especially many).
I didn't do full test, but when I try to "securely delete" a large zip file which is 6GB large, I need to wait a long time if I want it to be deleted. I cancel this, and revert to "normal delete", then, trash can cleaning takes less than 1 second to complete.
This could be useful if you don't want others using any sort of data recovery software to recover files you presumably don't want others to see.