Let's run the numbers, because that's how we avoid "sounds impossible to me", which isn't any kind of argument.
If we both have $100 Million, and you invest it here on Earth in a factory, with the expectation that you'll earn it back in 8 years, that's $12.5 Million a year.
Meanwhile, I put my $100 Million into *space* factories, which double every two years. [As mentioned, a "two-year doubling-time" is *on schedule* for a complete industrial process that uses 90,000,000 kilos of equipment to produce just 1kg per second of output, which is far *more* than we currently use!]
In 8 years, I've experienced 4 doublings - I have 16 times as much factory! So, now, my productivity results in a drop in prices for *my* products by 16-fold, *compared* to your Earthling factory prices. We BOTH see a drop in prices as supply increases, yet MY factory accounts for the lion's share of production, so I capture MARKET SHARE. YOUR *ENTIRE* INVESTMENT is now worth 1/16th as much, and your business goals are now irrelevant compared to mine; you earn *less* that $1 Million on your factory, while I still grab a full $12.5 Million each year from mine. So, whoever *doubles* space-equipment repeatedly is also the company that dictates the future of the market. All other competitors are *devalued* out of existence.
Finally, no, the demand for space materials is NOT equal to the demand by Earthlings. Companies make purchases from vendors, and their valuations are based upon future expectations of *comparative* success. So, the vast majority of metals mined in space will be used by those same companies in space, NOT by people on Earth.
Your argument that "supply won't grow because demand won't" is historically false - check what happened when we got energy-sources that were dozens of times cheaper. Demand shot-up a hundred-fold. It's a well-studied property of *real* markets, called "Jevon's Paradox".
You are basing your assessment on a "general feeling" - I'm basing mine on the numbers. I was spot-on about the impact of the Coronavirus, as shown in my article "The Coronavirus Market", among numerous other analyses I've done. Run the numbers, and you'll spot real trends; if you just "go with what makes sense to me" you'll always be behind the curve.
