Instructions for turning it off are in the article. Took me less than 5 minutes and it's already off.
Turn Focused Inbox On or Off in your organization
This example turns FocusedInbox Off in your organization.
NOTE: Your users won't see the Focused view until they close out and restart Outlook.
Connect to Exchange Online using remote PowerShell
You need to be assigned permissions before you can perform this procedure or procedures. To see what permissions you need, see the "Transport rules" entry in the Messaging policy and compliance permissions topic.
Run the Get-OrganizationConfig cmdlet.
Get-OrganizationConfig
Read the response and look for the Focused Inbox responses. Run the following cmdlet to turn Focused Inbox off.
Set-OrganizationConfig -FocusedInboxOn $false
You should see a response that FocusedInbox has been turned off.
NOTE: If Focused Inbox is turned off in your organization and you want to turn it on, run the Set-OrganizationConfig cmdlet with -FocusedInboxOn $true.