While autopilot is generally impressive on curvy 2 lane highways in Colorado, I am a bit surprised it doesn't hold the lane better. It often drifts to the center line, near on-coming traffic. This happens especially on right hand curves. I think computers should be better at this......
My experience with AP on curvy highways (interstate though, not 2-lane, so probably even less curvy) is that AP will in fact hold itself centered in the lane, but sometimes this is not desirable. For example, if you are in the left lane going around a left curve, passing a semi in the right lane, I think our natural instinct is to hug the left shoulder. Having the car maintain a perfect centering is a bit unnerving, to the point where my wife asked that I do the driving on those highways. I do somewhat agree with her!
I've been using "co-pilot" (I still can't call it "autopilot") in various iterations since 2013. Notwithstanding numerous software updates, I've noted little improvement in the ability to negotiate lane control at the crest of an uphill right turning curve. Invariably, the car drifts toward the center line, occasionally crossing it before correcting. There've been enough occasions that I've had to re-take control to avoid a problem that I don't trust AP on curvy two lane roads any more. And I, too, have noticed the tendency to 'drift' too closely to a semi when passing on a left hand curve on the Interstate. I would have thought by now that these anomalies would have long since been addressed.