In theory this is certainly true. In practice the most common experience is software where UI elements are completely unreachable from the keyboard, and/or have no label at all. If you talk to tech-savvy Blind people for a while you invariably hear things like "the app doesn't have labels but I know the third link is the settings page, so I just count until I hear 'link' 3 times". Most people aren't going to hire an outside person to test their project, and frankly I think that's often reasonable for personal projects and small companies. But if you exercise the UI flow yourself, at least you know it's possible to use it.