I wonder when PistonHeads hear back from MB that winter tyres need to be fitted whether they would be willing to put this to some kind of test as unless someone with clout does this debate will go on forever!!
As you are about to give your dealer £60k, I would think you are in a pretty strong position to get them to fit winter tyres FOC or at least prove they fix the fault.
Assuming they can actually source winter tyres for a C43