If I had to take a guess, I'd say some of those oddities you are dealing with (Primarily things like wide turns) has to do with G-Force limitations set on FSD. I learned while going up a mountain as well as down, that FSD couldn't handle it even going below the speed limit. While normal city driving, laws set speed limits far too low in my personal opinion, Mountain roads going up and down seem to set the limits far too high. If you see a van attempting to go the speed limit while taking the turns with no wind, you can visibly see them shift the opposite direction of the turn dramatically. If you drove a sports car, you could exceed the limits, but if you were in an SUV or Van and not used to those roads, you were driving 20% below the speed limit. The Tesla set at 40mph on a 45mph road going up the mountain side would hit a turn, start drifting outside of the lane and then yell at the driver to take emergency control as it could not maintain.
I'm guessing the same thing is happening for those turns. A wide turn allows for less G-Force while still going whatever higher speed you are making the turn at vs the vehicle reducing it's speed to like 5mph to make the turn without exceeding the threshold. It seems like they want to meet with the average person's expectations of how fast you make a turn, so you don't truly feel like it's driving like a grandma, while maintaining these G-Force limits, so that was their work around. I could be wrong, but just a hunch.