That’s really strange. Your experience with auto-steer and auto-lane change is completely different than mine. I drive in Phoenix, and do about 100 miles in an average day, mostly on the freeway. I find the newer version, since V9, of the auto lane change works very reliably, and almost never had any issues.
It does try to center when the lane markings disappear, but in the city this doesn’t happen. However, if you’re on the interstate and not getting off, why travel in the right one anyway? It would be nice if it could be told to maintain a spacing from the left side of the lane if it widens, that would prevent most of these issues you described.
I have found auto-steer to be one of the best features of this car, I just wish I didn’t have to always apply pressure to the wheel. Even if I am paying attention, the pressure is a PIA as you stated.
When I change lanes, I find the speed is a little slow for my liking, I wish I could speed it up, to not go so slow with aggressive Phoenix drivers. It does a good job of speeding up or slowing down to find the right gap to fit in. It does a good job of aborting if someone suddenly blocks your gap. I haven’t had a situation where someone blocks my gap and my return space too. I don’t know what it would do, but that’s why you are supposed to be ready to take over at any time.
Anyway, the Model 3 is my first Tesla, and I do truly love it. I feel bad that your experience was so much different than mine. I have to wonder if there is a hardware or software issue with you car that is making it perform so badly. Honestly, the experience in my car is just amazing. Back with version 8.x software this wasn’t always the case, but definitely is now. However, I haven’t driven in the last 4 weeks, maybe a recent update has caused issues. In the future please post the model of your car, and version of software when you write this up, and others can compare based on similar models.