So I don't think it's a "straw man" to point out the answer to your question is market participants want promises actually delivered upon which you now admit is entirely dependent on the "guys with guns" (and/or trust). By extension, blockchains don't actually provide a trustless or decentralized solution to the actual problems of finance. Actually knowing that your counterparty will send you oil isn't some unimportant detail of the oil barrel market which can be handwaved away, it's considerably more important than the implementation detail of the transaction record updates or whether brokers are involved.
You've moved more goalposts in this discussion than crypto has moved in the useful bits of finance.