I don't think you have driven the Mercedes Will is talking about. "Mercedes-Benz became the first car manufacturer in the world with an internationally valid certification for conditionally automated driving to offer such a system as an option ex-works for vehicles from series production" as the news item reports, so it's not included in the version sold at the car dealer.

Your claim that it can't drive "unless there is a car in front" refers to assisted driving in OTHER Mercedes models, and has nothing to do with what this article discusses.

Tesla is currently not able to let the driver disengage from the driving wheel, and Musk himself says the driver has to stay vigilant, which is not what happens at level 3.