I think this might be one of the root causes of our disagreement - different ideas of who can do what, and how efficiently. I look at the prospect of one kid outproducing the entire world rhodium industry, and think, "wow, that's a massive capability". You think "why not have them do something else". I think "why not have someone else do the something else".
I get the feeling it's also a difference in what we imagine the history and background of this crossover world is actually like.
Given this is an SMT world, assuming that Raidou Kuzunoha is still canon to its history, that would mean occult organizations like the Kuzunoha clan have been around Japan since at least 800 AD. The Abrahamic religious organizations in the West obviously for even longer. That means materials with supernatural or magical properties would have been a part of the world for an equally long time. Even if anyone with "the right tools" might be able to summon demons, not everybody has the ability or knowledge to make those tools. AFAIK, the Kuzunoha Clan's demon summoning tubes were only made or makeable by Kuzunoha clan members, other summoners had to use other means.
If such things were around 1200 years ago, there would've been other occult-related materials that were rarer or more valuable than gold too then. Rarer for sure, on account from not actually being available anywhere on Earth, but coming from other planes. It's just not many people would have known they existed because if we go by SMT logic, this occult side of the world would've always been hidden from the public. Demons would've been the stuff of myth and nothing more.
But there would always have been stuff rarer than the rarest mundane materials and my assumption is that - yes, there WOULD actually have been occult sweatshops that made money dealing in the production and manufacture of such things, catering strictly to occult clientele. And making a boatload more bank than they ever could churning out mundane materials.
Or possibly, just don't usually have time to waste making mundane stuff, because while rhodium can be sourced from mundane mines, if you don't have all your mages cranking out the exotic sorcerous metals you need for those Dragon Stream Broadcast Tower machinery, there's nobody else in the world who will be able to supply the necessary materials.
And those Dragon Stream towers really needed to be set up yesterday.
EDIT: Again, "Dragon Stream Towers" is just an example - today, it's Dragon Stream Towers, yesterday it was Humpty Locks and Dumpty Keys, the day before that, it was Magatamas, the day before that (before they figured out how to make cellphones do it) it was COMPs, the day before that it was Demon Summoning Tubes, etc.
There would always have been some occult item or equipment requiring rarer-than-rhodium occult materials that only special people could produce and it would've been a waste to have them make gold or diamonds when they were the only ones who could produce the materials needed for those latest, state-of-the-art occult artifacts that everybody needed and would pay more than anyone would for the equivalent mass of rhodium.