WASD is 4 set directions, The anologue stick can move in angles and slight angles.
1) You can push more than one key (forward + strafe left for example) in order to move in angles. Rotate view up-down-left-right keyboard keys are mostly unused, as that is handled by the mouse.
2) You can configure other keys, you know. It hasn't to be WASD (which I hate personally). I use the keyboard arrow keys for movement, jumping and one "special key", and some keys of the numberpad for misc stuff. Never ran out of keys easily at hand to configure in all the games I've played
Same can be said for the camera, Mouse is irritating. The screen would move when I'd want to click on something and having to reach over from WASD to L for skills or whatever else has no fluidity to it.
With a little practise, and a little basic hand-eye reflexes, you can do precise jobs with the mouse. In fact, it even becomes
logical to choose the mouse over a gamepad for precise jobs, as with the more practise you've with it, the quicker you can get things done, and the most precision you obtain.
An anyways, virtually all games have a "Mouse sensibility" option, to reduce mouse speed in game and improve precision for those unfamiliar with it.