Correct, the IRS is capable of perceiving how an asset
can be used, but they are not capable of unilaterally declaring the classification of an asset. Currently, when it comes to determining whether an asset is a "currency", it has to be issued or used by a recognized nation state, or Congress has to label the asset as such.
Congress could easily delegate additional discretion to the IRS, they just haven't yet as they have been unprepared for this outcome.
When you look at the universe of assets, they either exist in walled gardens (brokerage accounts that there is no expectation to withdraw from, or that you simply can't withdraw from), are not easily divisible or have separate denominations if they were, or are impractical to transport (a barrel of oil, other spot commodities), or are not fungible (art, collectibles, barter assets).
All crypto assets transcend and overlap with the fungibility of every other asset class all at once, while being able to function as non-fungible assets if desired.