I have experienced some of the problems you’ve listed, but the dire impression you leave is counter to my own AP experience.
I’ve driven long distances on the interstates using NoA in no confirmation mode, average speed based lane changes, and no lane change warning other than the sound of the turn signal prior to making a lane change.
The performance of AP depends a lot on traffic density. The thicker the traffic, the more I have to override AP’s decisions. Personally, I’m impressed with its lane changing ability, but it’s not perfect. I sometimes have to push on the accelerator to hasten the maneuver. A move into the passing lane with a car approaching from behind at a much higher speed use to be a real problem. It doesn’t happen as often, but when it does I will to cancel the lane change before AP aborts the maneuver itself which can be a bit disconcerting.
Merging with on ramp traffic works pretty well. AP tends to slow down if there’s a car right along side. This works when the driver of the other car takes the hint, but not so well when the driver slows down themselves, and AP doesn’t respond by accelerating to make room behind. I’d like AP to move over if the left lane is clear. I think this is something that is being learned.
I rarely miss exits or interchanges these days. Where I do have to intervene, the error is consistent. It makes me suspect that the map data is in error which AP depends on to navigate. It could also be due to GPS location inaccuracy. Map errors may also be the reason AP gets confused executing driver initiated lane changes on some sections of secondary divided highways for no apparent reason. The symptoms are extreme tentativeness in executing the maneuver on a consistent basis on certain sections of those roadways.
AP is getting better and better at driving through construction zones. I used to have to disengage when entering these areas, but lately it manages quite well even when the lane markings are not clear. Lane position also seems to be improved when driving on wide lanes, and when passing semis.
I’m still using AP hardware 2.5, so I think some of the difficulties AP has are simply due to the limits of its processing capacity. Approaching cars and trucks are rendered on the UI quite well at times, and at other times, not well.
The rate of AP improvement has been slow to date which justifies a prediction of Q1 2022 for FSD. I would have put the date a year earlier, but that’s based on what I know about Tesla’s AP development strategy plus a large dose of wishful thinking.