The optimal route means picking up multiple people on the same route, and dropping them off elsewhere on the route, and then making the vehicle large enough so that they can do this comfortably, i.e. a bus.

It ends up being another form of public transport — perhaps one with no predictable timetable, or perhaps timetables are themselves a useful Schelling point, I wouldn't want to guess.

But as fixed bus routes make it possible to plan things like bus shelters, I think I'd prefer a bus over the logical progression of self-driving "taxis" that constantly move rather than finding parking spots.

That's optimal for the vehicles, but less optimal for the people, who have to walk to stops. I used to live in Germany which had fantastic public transport, but walking a mile to the nearest stop was something we took in stride. That's great for health, but didn't prevent Germans from being quite fond of their personal automobiles, and there didn't seem to be noticeably less traffic than in the US.

Meanwhile I think plenty of people find Uber perfectly convenient, just a bit expensive.

As far as physical efficiency goes, Tesla's plan is more efficient than their competitors'. Their dedicated robotaxis are either small two-seaters, or decent-size buses.