I was assuming the opposite. Keyboard and Mouse is usually regarded as superior to joysticks for FPS so I assumed they were trying to bridge the gap and come up with something more mouse-like?

Yes, in fact it would solve the aiming issue, while using the left trackpad in "joystick mode" would better replicate a keyboard.

If it were me doing it, I would use the trackpad and the trackpad buttons. (I'm not sure, but I believe each trackpad is "pressable" and has multiple buttons, replicating a d-pad)

I would tap and drag for little and precise movements, swipe for fast movements, and press the button for default movement. With some training, it can become pretty natural.

You'll hopefully be able to choose based on preference, since choice seems to be the theme here.