Re: As much as tape has often been the bane of my life...
If you've got 100 TB to store and your on-premises servers are already in a class 8 datacenter, LTO-9 may make sense. I agree 100% about the lack of storage management; very few organizations that need to hire librarians are aware of that fact, and even the ones that are don't hire enough.
Documents that aren't personal should be stored in SharePoint folders instead of OneDrive.
(I'm a Microsoft employee but have no connection to or knowledge of M365 pricing or really almost anything that isn't public. If I had been offered Azure Blob Storage archive tier1 in Government Top Secret ten years ago when I had LTO-4 libraries, you bet I'd have been camping out in the procurement people's offices until they let me click the buy button.)
1 Or the AWS/GCP/OCI/IBM Cloud equivalent. I left that position in 2013, when Amazon had just signed the first classified cloud computing contract with CIA and Microsoft was still calling it Windows Azure.2
2 For reasons I still don't understand, it has been a low single-digit number of days since I've seen the phrase "Windows Azure" used in a production system, and it needs to stop.