To create a feature I must link it to an Epic before I can save it, but then I can go back and unlink the Epic. If I can go back and unlink the Epic, then why not allow the user to create a feature without linking it to a specific Epic from the beginning?
This is an account level customization. By default, the epic field would not be required when creating a new feature. Your account administrator can update this if needed. This article explains the custom layout capabilities in more detail.