That's the correct indicator to look for: the number of Waymos on the road is still very small compared to the number of other vehicles. Alphabet wouldn't risk the cost of expanding to the current number of cities without very strong confidence that they're not going to lose their shirt doing it.
The evidence so far is that they are throttling demand by keeping the prices above that of an Uber. It's definitely still an experiment. If the experiment is successful, expect to see more cities and more vehicles in each city in expanding service areas.
There are step changes that have to be made to keep waymo expanding. The tariff situation is blocking plans to have dedicated vehicles from China. That has to get sorted out. The exact shape of the business model is still experimental.
Of course it's got to be safe. But there are dozens of dull details that all have to work between now and having a profitable business. The best indicator of a plausible success is that Waymo appears to be competent at managing these details. So far anyway.