"This incredible range will be achieved through efficency improvements rather than just a bigger battery pack."
What an interesting statement! "Bigger" – compared to what? A Tesla Model 3 Long Range AWD? That can do around 296 miles (EPA/Highway) – so the Mercedes-Benz will need to be 2,5x as efficient.
The drag coefficient is one area that could be improved. C(d) for the Model 3 is 0.23, which is pretty good for a production car. Lower than that and you are in experimental territory – which is probably how this project might end up for Mercedes-Benz.
Not bad, because these types of projects usually teach us something new. But not good, since this will be another "promise" broken, due to this inflationary PR-approach.