"I’m interested in an easy backup-out-of-aws solution."

rsync.net has 'rclone' built into the environment[1] so it is trivially easy to call rclone, over SSH:

  ssh user@rsync.net rclone s3:/some/bucket /rsync/account

... and perform arbitrary data movements into, out of, and between S3/glacier/nearline/gdrive resources. Your "out-of-aws solution" contains ZFS snapshots, on any schedule you like, so you can just do a "dumb" sync to rsync.net and handle the retention with the snapshot schedule.

Also, the snapshots are immutable (read-only) so your data gains some protection against ransomware and other threats like accidental deletion.

You should trust us with your backups because we've been doing this since 2001.

[1] https://rsync.net/products/rclone.html