It depends on what the goal of the DRM creators is. If their goal is to prevent copies that most people would consider watchable, then they would not consider the iPhone to defeat the DRM. But some screen recording technique with framerate sync would defeat the DRM. If their goal was to prevent sharing of the original compressed stream, then they would consider even screen recording to not defeat the DRM.
Why do you need a car when you can walk? Why use encryption when you can physically hide things? The answer to these questions and more is that when it isn't about faster/better/cheaper, it's about improving quality of life. Be it increasing privacy, or removing undue burdens.