There are several good and not so great ways to do off boarding from icloud.

- Use a mac. - If you have your photos on your ios device you can connect it as a camera to windows or linux and copy the files off. - If you use google photos, onedrive, dropbox, synology or any other file storage app that can auto upload photos you can do it that way - you can install icloud for windows and use that to sync photos. Its in my experience super slow for large amounts of photos but works. - You can request zip downloads from icloud. - You can initiate a server to server transfer from icloud to google photos.

When I had to move a large amount of data from one cloud storage to another (migrating Dropbox and Mega to Google drive) on slow dsl internet, I rented a VPS for a couple hours from Digital Ocean and installed a desktop, which I connected via x2go. If you have the ability to do this, your home internet connection speed is irrelevant.