You forgot the part where even though you carefully do NOT use Sharepoint at all, it turns out Teams uses Sharepoint as the backend store for "files" and now you have a mass of files in Sharepoint you didn't even expect.
You can turn off file handling all together in teams, which it sounds like you should have done.
End of the day, SharePoint is cheaper than a file server as you get a file solution a MVP discovery solution, and a MVP workflow engine that is good enough to get started, but lousy enough to sell Dynamics or PowerWhatever.