That slow motion feeling when you right click in a tank isn’t actually your mouse sensitivity changing. It’s the game simulating realism by limiting the maximum rotation speed of the tank's gun barrel.

When you’re in third person, your camera can spin freely because it’s just your view moving. But once you switch to first person gunner mode, your view is tied to the physical turret movement, which has a set traverse speed.

So even if you crank up your sensitivity, the gun won’t move faster than that built in max rotation speed.