If you drop the utilization, the cost of the driver as a percentage probably goes up a bit. But here's the thing about those numbers.
Yes, driver salary is a big chunk of taxi cost but flip things around. It's only about half the cost. In other words, there's this widespread assumption that autonomy totally changes the nature of automobiles and automobile ownership even though it only cuts the cost in half.
Ask yourself. If you own a car today, would getting a 50% discount on taxi rides completely change your behavior. Maybe it would for some at the margins but only at the margins.
Look longer term.
Parking spaces in cities cost ~30k. (And in some cities, a lot more than that). Included with a house, they are still part of the price (no free lunch).
Over a 30 year mortgage, that is 1k a year.
In California, car insurance is almost 2k a year. (Oddly enough, 1.1k in New York State!)
So 3k a year just to have the privilege of driving a car.
Apparently an average new car now days cost 31k. (Which seems insane to me, but that is what people are buying).
Being generous and rounding down a bit, that is another 5k a year.
So now 8k a year, before gas, before maintenance, before any warranty problems, before screws in tires, etc.
If mass transit can replace commuting to work, then weekend outings with automated taxis become very doable. If you give $5 per ride (on par with UberPool, though I realize that isn't profitable), it is 1600 rides a year to break even with owning a car. (Though ownership goes down after the car is paid off, 600 rides a year to break even!)
2) Especially since amortization cost is also reduced, you might as well electrify the vehicle (this requires some sort of robot arm for fast charging, but I suppose you could pay someone like $0.50 per cycle to plug and unplug a bunch of vehicles in the interim). That reduces fuel costs by a factor of 2 and maintenance costs even more.
3) No driver means room for more people or ability to shrink the car, reducing all the above costs.
So you've now reduced all the other costs by a factor of 2. That means your overall costs are now reduced by 75% or more. Yeah, that's starting to look pretty attractive.
IMO the killer app is in freight anyways.
On top of that, the space and interfaces for the driver is a substantial part of the cost and weight of the vehicle itself.
Driver salary is 26% of the cost of trucking.
Driver salary is 52% of the cost of a taxi.
Those numbers are in the single digits for aircraft and trains.
We could replace pilots and train operators, technologically speaking. But the incentives are not (yet) large enough to overcome the regulatory and cultural barriers. We'd rather have that extra order of magnitude of safety, because it costs so little compared to other expenses.
The cost/benefit calculation for drivers is fundamentally different.