They seem to be scaling just fine. Here in SF they're ubiquitous and most people I know use them regularly (and usually prefer them to rideshare). Sure, it's not the type of growth possible with pure software, but they're doing 500k rides/week and are looking to be doing 1MM/week by the end of the year. What scale does this business need to be for the author to consider them a real company?
While true to date, this can't go on literally forever. Waymo has to somehow bridge the gaps between hype, revenue, and eventually profits that justify the valuations (i.e. "grow up"), but they have a huge advantage to do this: their tech actually works. The moat isn't just capital availability, they solved a very hard problem, and that will protect them for a while going forward.