I agree 100% with this reasoning. This camera was, as far as I can tell, designed to overcome some of the shortcomings of the original blink camera that made it not the best option for outdoor use. From what I've read (mostly in the smartthings forum), PIR motion sensors can be difficult to use outdoors.
A solid motion sensor is a basic function of this battery powered camera. Without it, the camera is useless.
Some of the other options mentioned seem totally reasonable to pay extra for on a monthly basis, particularly the 4G backup.
But personally, if I'm ever asked to pay extra for a feature that is a basic component of how the camera is intended to function (i.e. accurate motion detection that triggers recordings), that'll be the end of my experience with Blink cameras and I'll encourage others to look elsewhere as well to avoid being nickel and dimed.