Legal Hold and Retention isn't Archive
Surprised Microsoft is in this at all. Legal Hold and Retention Policies are neither a backup solution nor an archive solution. Even just accidently turning a policy off can wipe all retained data, it relies on document versioning for any form of rollback. A true archive should be able to answer the question "What did person X's data look like on some date last year, I think they're covering something up?" don't think MS can do this in 365.