The robotaxi evaluation only made sense when they claimed to be years ahead of competitors. A robotaxi service operating in a regular taxi market could have large margins. But Waymo is already operating, any Tesla robotaxi company is going to compete away all the margin with Waymo.
As I understand it, Waymo is restricted to areas that it has mapped extremely well, i.e. major cities.
Which also happens to be where most of the money would be, so it's probably a good bet. Tesla seems to be hoping to displace Uber in the suburbs, while being an also-ran against Waymo in the denser downtowns. That includes ferrying a fair number of people into and out of cities, where Waymo can't (currently) go.
That's probably not as lucrative as Waymo's core market, but it could have some decent margins.
