Welcome to what we have been suffering with since release. Asobo have decided to implement a kind of negative mouse acceleration. Sadly this is something PC users see a lot with some of the worst console ports.
If you compare a mouse, and a console controller (analogue stick), the mouse uses absolute positioning, and the joystick relative. You move the mouse, and the pointer “should” move at the same rate that you move the mouse. With the joystick you deflect it a certain amount, and the thing you are controlling continues to move by that amount, increasing in speed if you deflect it more, or stopping if you centre the joystick.
My guess is they have implemented this negative acceleration to make small joystick inputs more precise? The problem is they applied this to the mouse controls as well! It is entirely possible for me to drag my mouse slowly across my desk, and not have my view on screen shift an inch. Until you move the mouse a certain speed your viewpoint won’t change.
I hate this with a passion! 
They really should uncouple the mouse, and controller schemes, and leave the mouse inputs alone, and stop interpreting or otherwise fiddling with them.
These symptoms are one of many that come under one of many umbrella terms, including consolitis. PS I apply this to the controller itself, not the platform.
A good developer is one that understands they have two audiences with two different controls schemes, and implements both of those in an optimal manner.
There was a test we used to do to detect regular mouse acceleration in a title. What you did was position your view at a fixed point on screen that you could identify, and make sure the mouse is butted up against something, like the edge of the keyboard. You then move the mouse away from that point at a different speeds, and back to the keyboard. If your view returns to the exact same spot you have no mouse acceleration. If you vary the speed that you move the mouse between tries, and if your view does not come back to the same spot you have mouse acceleration.
That test would work well here, but is unnecessary as it is so obvious it is in effect.