You are assuming the motivations behind these decisions are purely based on safety rather than a philosphical difference in approaches.
From a practical standpoint, liability needs to be all or nothing. You can't have a driver worrying about whether they are going 40mph or 41mph. You can't immedaitely give the driver liability if it starts to drizzle or the sun sets.
Mercedes is taking the approach that they are always responsibile. Other manufacturers are taking the approach that the driver is always responsible. The end result is that the Mercedes system is much more conservative in how it can be used. This says nothing about the quality of their technology in comparison to their competitors. It simply says they are focusing on the easiest problems first while their competitors are taking a more holistic approach trying to design a system that has more broad usability.
As everyone knows by now, literal full self driving (as in get in your car, tell it to take you to the other end of the country and wake you up when it gets there) is entirely out of reach to current technology, and will stay out of reach until we design new sensors and possibly general AI*.
So, the current goals must be to achieve something similar in certain well defined limited conditions, and with reliable automatic checking that you are still within those conditions - hopefully conditions that one is actually likely to encounter. Until we have that, letting self driving cars on public roads is a menace.
Current self driving cars are at best at the level of a driver going through their first driving lessons, and one with very bad eyesight at that. Having a human act as the driving instructor, theoretically prepared to step in whenever the AI makes a silly mistake, is not enough to make these cars as safe as the average (non-drunk, non-sleep-deprived) human driver.
What Mercedes seems to be doing is responsibly pushing the state of the art further. Having a car that is safer than a human driver without depending on your constant vigillance is a huge step forward. Obviously, this only works in certain conditions, but the car itself detects when those conditions are no longer met, and gives you quite ample warning to assume back control.
* Elon's shameless lies about having your Tesla act as a self driving taxi and generate a profit for you while you work in the coming years have well been put to rest.
From a practical standpoint, liability needs to be all or nothing. You can't have a driver worrying about whether they are going 40mph or 41mph. You can't immedaitely give the driver liability if it starts to drizzle or the sun sets.
Mercedes is taking the approach that they are always responsibile. Other manufacturers are taking the approach that the driver is always responsible. The end result is that the Mercedes system is much more conservative in how it can be used. This says nothing about the quality of their technology in comparison to their competitors. It simply says they are focusing on the easiest problems first while their competitors are taking a more holistic approach trying to design a system that has more broad usability.