This is a non-sequitur - there's absolutely no expectation that space mining would result in the cost of any available raw mineral dropping by at least one order of magnitude; it's not a solution for "cheap mass mining" solution, it's a solution for very expensive targeted mining of something that we need very much.

The parent post argument is that we can get as much gold as we need on earth with techniques that aren't used because they're too expensive, but even those would still be far cheaper than space mining.

Space mining can be solution to prevent the price of some rare earth material skyrocketing in the future because we're running out of it, or to get something that's very rare and expensive (it's just that nobody has a clear proposal on what it's going to be) but at the moment gold is too common and cheap to justify the expense of mining it in space.

At current costs it would be a waste of money to pick up gold bars orbiting Earth; after (if!) SpaceX Starship cuts down cost of bulk transfers to orbit ten times, then it may become economic to bring down certain exceptional cases of highly concentrated rare materials - but it certainly will not be cheaper than the price of any raw minerals that exist on Earth in reasonable quantities, such as gold ore (alluvium ores, which aren't that valuable by weight due to low concentration in gold)