But you're missing a point that's true of the startup metaphor but not of the mercedes one: "uber for x" has been absolutely beaten to death as a low-effort startup pitch, to the point of being a useful counter-signal. Mercedes has no such baggage when it comes to judging the people saying the word.
I disagree. Using "Mercedes" instead of "taxi" changes the framing (using "taxi" would have evoked "oh, it's a taxi app; thse already exist"); describing something as "Uber for X" does not change the framing (aside from the known fact that it has become a tiring cliche).
Ultimately, writing that one sentence with unmph is harder than it looks. Sometimes "Uber for__" is concise and conveys lots of meaning, sometimes it's vague and meaningless.
I think the biggest trap in the "A for B" formula is trying to ride on the prestige of B. That's why there are so many "Apple of X." What they're trying to convey is "awesome, stylish & successful" or somesuch. It's like calling yourself "Michael Jordan of __". You're just being obtuse in telling me that you're awesome.
"Uber for tripsitters" OTOH conveys actual meaning. Press a button, a freelance tripsitter will arrive.
Similarly, I think, when people say "Airbnb for something", they're using shorthand for something with a lot of prior meaning attached to it.
My point: we're being too harsh on those who use "Uber for this" or "Airbnb for that"... they're using shorthand the way Kalanick used "Mercedes".