Who really thought Valve making a controller would make an unusable one? This was never a concern. The concern here is that it might work well with FPS, RTS etc... (or good enough)... but might not work as good as button based controllers for other genres.
However, playing a FPS on anything but a Oculus Rift or equivalent is going to feel quaint in a few months.
If by ratcheting you mean the repeated movements to look around, that is very similar to moving a mouse with a low sensitivity settings.
It's intended to take the gaming pc (and by, extension steam) out of the man-cave and into the living room to compete with consoles. This requires providing people with an ability for people to play FPS and RTS decently with a controller, rather than a mouse, or they are going to stick with their man caves and mice.
Also I guess difficulty in singleplayer games would have to take the control scheme into account.