There are certainly lots of files in the Preservation Hold Library but they are very difficult to get at. Two keys to any backup solution is the ease and speed of recovery and I don't see it here. The Overview of retention policies is long and has lots of very useful information but I don't see one word on how to make use of the information that has been retained. In all my searching I have found lots of information about retention but nothing on how to access the preserved data efficiently.
However, having said that, we had a case where an employee left and came back several months later. He requested the contents of his old mailbox which had been deleted. The mailbox was within our retention period and we were able to get his old information and merge it to his new mailbox. It worked like a charm! It was quick, easy, and accurate.
If there was a similar process for retained SharePoint and OneDrive for Business files I might agree that it is "beyond backup".
Thanks for your article and comments.