Ivan we've just completed rolling this feature worldwide and overall this increased engagement.
At a high level I see two sets of users, ones that are fairly new to files and not used to viewing files in a structured matter, and ones that have been around for a while in the workplace and grew up looking at files from a file share lense with folders and subfolders. While I can see advance/mature ECM users to see gaps, new users find what they need in a flat view with files sorted by most recent modified date. Agin two key differences from a SP docblib, about this view is that it lists ALL files (not just the ones stored in the SP doclib but also all attachments for instance), and it shows the email thread associated with a file, are your users aware of these differences? Do they systematically put all their files in SP or some still email attachments?
We are not sitting still on this topic of files and email and plan to deliver a number of updates to address feedback and continue to help users easily work on files & emails.
To answer your questions below:
1- yes files are sorted by modified date, we plan to make this more obvious.
2- see above (we are showing all files + email tied to files), you can easily navigate to SP doclib from that view. Good point on Planner and it's something we are working to improve as well.
Regarding your last point, why would it be more complicated?
