I'd say about 90% of the time I get the dreaded "However, we were unable to create a copy of all your files" message in the takeout email.

After multiple retries, it eventually succeeds but it's a manual process and using this for regular backups is extremely time consuming and frustrating.

Going through the process just once is definitely doable though :)

Can I ask how exactly you went about doing that? I would like to try iCloud for photos, but how did you manage to combine the image files Takeout gives to you with the metadata in the JSON files?