You could have used the exiftool -overwrite_original option to get exiftool to delete the "_original" images for you. Also, you could speed things up a lot by calling exiftool only once. If there are no spaces or other special characters in the file names, this could be done simply with:

`exiftool -subject= -keywords= -overwrite_original @ARGV`

But for a robust script you should do the necessary escaping and/or quoting of file names first.