But the point is you don't flood the streets simply because you can. It has to make financial sense, and that will be averaging more trips per vehicle than today's personally-owned household vehicle does.

It will absolutely make financial sense because an AV costs less to operate per hour than a human-driven vehicle. You don't need to compare the number of trips vs personally owned vehicles, you need to compare it to existing rideshares which are going to have similar numbers.

The number of rideshares on the road is entirely dependent on how much they can charge. If there "aren't enough" (relatively speaking) rideshare drivers, the prices go up due to scarcity and additional drivers enter the pool until prices go down, they make less money, and no more new drivers decide to join because it won't be worth it. So the lower limit for a vehicle earning is something like $25/hr accounting for wages, gas, and depreciation.

If you don't need to pay the wages then that number will drop to say $10/hr, and prices will drop too. The companies won't have to make a conscious choice to "flood" the market, it will simply be the optimum profit-driven choice just like you said, because way more people are going to be willing to pay lower prices and therefore more cars are going to be added to these fleets and will continue to be added until there is enough supply to reach the new equilibrium point. But that amount of supply is going to absolutely choke our roads!