The precedents set in that case mean that the liabilities arising out of legal action based on 'strict liability' are likely to be extremely punitive (these days, well upwards of the $147M awarded against Ford in 1980, and into the billions). Any company that did not factor such a payment in their calculation in addition to the indirect costs of reputational damage, deserves everything they get. I doubt this is the case with Mercedes.
One question I do have that perhaps someone here will know - is the Mercedes guarantee limited to certain locales? e.g. Germany only as the roads there are in good condition and well marked? (I'm assuming here).
Think about it like this: company A says “our government product is military-grade. We have a 1 year warranty.” while company B also says their product is tough but offers a 5 year warranty. Which one do you think has better data supporting the durability of their product?
Has no one watched Fight Club and heard the anecdote about how a company will only recall a car if the cost of the recall is lower than the cost of settling all the lawsuits? All this guarantee tells us is that Mercedes did a similar calculation. Taking legal liability is not proof the car is safe. It is proof that they think the value of customers thinking the car is safe is more valuable than the cost of paying out settlements. Tesla not making the guarantee does not prove their cars are unsafe. It is evidence that if they did the same calculation, that got a different result. Maybe that is because the car is more dangerous, but it could also just be a different marketing philosophy and Tesla notably does not approach marketing like most other car companies.
The conclusion that you reached in which the Mercedes is safer than the Tesla is valuable to Mercedes and that opinion was indirectly purchased by Mercedes paying out legal settlements.