We don’t back up the resized / thumbnailed images by default any more, just the original image.
This means all backups are smaller, but restoring a backup is a bit more work in the short term, since after restore the system now has to auto-regenerate the “optimized” (resized, thumbnailed, etc) copies of the images from the originals. That’s the tradeoff.
Did I state this correctly @sam?
There is also a site setting if you want to retain all resized images in the backups to make restoring a bit more efficient.