This was my strategy too, but with a disgusting script which quit photos.app, rsync the photo library to a network share, then reopened photos.app so that it kept downloading from iCloud.
Not sure if the open/close is required, but I didn’t want to find out.
I don’t fully trust iCloud Drive / Photos therefore I use FSViewer to download all photos from my iOS device du jour (making sure to keep the HEIF formats), this way I get the Edited (slo-mo, live, portrait, usw) and pristine versions as Jobs intended. All kidding aside, after the gray area gate of 2017-2021 I had to find a more reliable backup workflow. As of today I only use iCloud Drive / Photos to extract some RAW photos that for some reason some picky apps don’t save to the photo album (looking at you ProCam 8.0). I made several tests including hash comparisons and imagemagick diffs and I am quite pleased.