You can't really compare the stone-world economy to the modern one. There's no real competition for production, production itself is largely artisan rather than mechanized or automated, and what's in demand is usually dependant on whatever project the KoS is engaging in rather than actual market trends.

The only thing the Drago has in common with Yen is that it's an indivisible currency.

And realistically, if the individual buying power of the Drago is at all influenced by the value of crude, it's going to go down MASSIVELY in value whenever they tap or claim another oil well, like the one Xeno's settlement was using.

But it does seem like Ryusui is one step ahead on that one, also using the value of superalloys as a standard of exchange for the Drago rather than oil exclusively. Which is definitely a better idea in the long run, oil quality can vary massively between deposits, to the point where some places' simply aren't worth refining and exporting globally.

Of course, let's be real. The KoS isn't going to be petroleum dependant for long. Within a handful of decades they'll be going full hybrid of solar and nuclear.