I ran the numbers, and for most non-braindead cities something like a fleet of 6-seater minivans will easily replace all of local transit.
And with just 6 people the overhead if an imperfect route and additional stops will be measured in minutes.
And of course, it's pretty easy to imagine an option to pay a bit more for a fully personal route.
you made too many false assumptions if you came up with those routes. Experts have run real numbers including looking at what happens in the real world. https://humantransit.org/category/microtransit - (as I write this you need to scroll to the second article to find the useful rebuttal of your idea)
This exists in a way -- I'd wager every city has a commercial service that will shuttle you to, say, the airport. They're not cheap, however.