There's a simple reason for each of these steps.
1. If you don't remove both Outlook apps, Windows Update will replace them with the New Outlook app.
2. USO Scheduler has a hidden task to install the latest Outlook, regardless of whether your image has any Outlook apps.
3. Even if you followed Steps 1 & 2, OOBE tries to force the new Outlook on your system. To block this attempt, you will need to temporarily block CloudOptimizedContent, which has the same effect of disabling Content Delivery Manager.
4. After OOBE has completed, there will be no further attempts to install Outlook. Therefore if you like, it's safe to re-enable CDM at this time and allow it to perform the usual tasks.