And the non-Google engines can't even begin to solve use cases that I find central to my search experience, because the Google results are based on user signals

And the non-Google engines can't even begin to solve use cases that I find central to my search experience, because the Google results are based on user signals that the other engines are incapable of processing, even when I am logged in. For example "When is the bus coming" does what I want on Google, does nothing of value elsewhere.