Failing upwards would be her announcing she's raised money for a new start-up at which she will be CEO. (EDIT: To be clear, I'm agreeing with you.)
Instead, she's going back to where she has a track record. It would be like Musk selling Twitter. Or David Marcus going back to 2001 [1].
Isn't it fair to look at share price under their leadership? What other objective measures do we have of their management abilities? We take the OP's word for it that they're the best? Or is this like sports teams recycling the same 30 coaches?
This.
The valley is nothing but a machine. Feed young engineers in one end and spit unicorns out the other. The same players make it all go.
The platform shaping communication is a fact, but not a license to use it to program a worldview. The job of a general-purpose platform is to enable communication, but otherwise stay out of the way.
I don't use it a lot. But my Nextdoor is basically pictures of animal sightings, pictures of pets who got out and pictures, a few hours later, of them being found.