The hand waving is probably reasonable for a couple of reasons. The first is that you can't really math things out yet when costs are shifting by orders of magnitude on relatively short timeframes. What seems impossible in one year is a casual achievement in the next. If we go back to 2002 (when SpaceX was founded) and I told you that within 2 decades they'd have lowered the cost to get stuff to space by more than 97% relative to Space Shuttle, it'd have sounded somewhere between unreasonable and impossible, yet that is exactly what happened. And Starship is set to send prices plummeting yet again.

The second reason is that the notion of economics becomes kind of odd when you start introducing space. Space has practically infinite resources of every type imaginable. For instance one single asteroid, Psyche 16, is thought to have orders of magnitude more gold than has ever been extracted in human history. But I mean, what does this even mean economically? Obviously if you start bringing back hundreds of thousands of tons of gold, the price is going plummet. And even the viable possibility of this happening would probably send the price of gold plummeting. So... it's weird. We're in uncharted waters.

And then on top of this access to space will mean we will start expanding outward - colonies, vastly larger stations stations, and so on. And these expansions will develop their own parallel economies with their own needs/production/etc. This is all kind of like trying to predict the economics of the internet before the first cable had been laid.