Why implement a temporary fix when this option is clearly not functional for a large majority of users? The toolbar on the side of the screen takes away space, is inconvenient, inefficient to use, and must be compact. This is also why I will not use the web-based version of this application, or other Microsoft programs.
Someone posted a registry edit that moved the toolbar to the bottom again. I'm not sure who or where that solution is but this is what I did and it worked:
open RegEdit as an admin
navigate to HKeyCurrentUser/SOFTWARE/Microsoft/Office/16.0/Common/ExperimentECS/Outlook
Add a new string if this one isn't there:
Microsoft.Office.Outlook.Hub.HubBar
set the data value to False
I always recommend a backup of the registry as changing the wrong thing can have detrimental effects. However, this solution worked for me and did not cause any problems. I've set it on three computers now.