There are a few things I think you've overlooked:
- For one, you're talking about human drivers covering first and last mile, which is a tiny, tiny fraction of the route that a truck covers which is why the Starsky model works well, in theory anyway. That means one given driver can do the work of probably a few hundred trucks in their last mile phase, even if they end up with some downtime in the middle, it's not even close to balancing. You're still talking about a possibly slightly larger market being overseen by a much smaller workforce.
- Secondly, this completely ignores what could be the silver medal effect of truck driving becoming automated; the death of millions of small and large businesses that operate basing heavily on the incomes of truckers, everything from truck stops and diners, all the way to motels, specialty truck accessory companies, on and on and on. These are the ripple effects that many people aren't looking at when they're thinking about this, it isn't just trucking, it's one of the last jobs available to you with naught but high school under your belt that earns around $40k. And that's not even going into how many businesses do a ton of business with truckers that earn that wage, which is usually much higher than their neighbors are earning.
- Thirdly, if all trucking is done from various Starsky-like operations, then truckers in general will be moving into more consolidated living conditions. Again trucking is one of the VERY rare jobs that requires minimal training, pays a comfortable wage, and is available pretty much anywhere in the States where there are roads and people who buy products. If you want to work as a software developer, chances are you'll have to move to Silicon Valley, San Francisco, Austin, etc. but if you're looking to be a trucker, you can go pretty much anywhere and have fairly solid employment opportunities. For now.