The point of ACC is not Autopilot. It's not intended to take over steering and control fully for you. It's meant to reduce driving efforts, but you are still driving.
If you know how to use it, may easily cross 100+ miles without touching the break or gas pedals. This reduces strain and stress as you still drive, but the car manages a good chunk of the 100s of small adjustments each minute.
If you are observant enough you can drive only by changing ACC settings, letting the car manage things.
I wouldn't trust any vehicle to drive me in the day and age. They are unreliable and unsafe. I do trust for them to relieve some of the load though, and for 140k+ miles have never let me down once, so that's a pretty good record I'm my book.