Just give us a ‘download all’ button with the ability to resume in the event of a failure. RSync has been around for a long time why reinvent the wheel for every different service. Welcome to Modern tech - constantly reinventing (square) wheel
This exists if you have a Mac. Set Photos to "Download Originals" in the settings and every photo will be downloaded to the "originals" directory in your photo library bundle.
It helped me free up iCloud storage without filling up my SSD (which is what would’ve happened if I synced the whole library using Photos). I pointed icloudpd to one massive album with random Filmic footage, which I then transferred to external storage. Download took multiple runs due to size and network interruptions, thankfully the tool avoids redownloading already completed items.
[0] https://github.com/icloud-photos-downloader/icloud_photos_do...