>> a reasonably good explanation of why, at least in my opinion, crypto is still completely non-viable as a real medium of exchange

The way I see it, the reversibility of ACH is mostly a 'workaround' of ACH's security flaws. If a crypto does not have security flaws, then it does not require such workarounds. The only drawback is that it cannot correct for human error. But IMO, I don't see human error as a major issue since it's a reality of life that people should be responsible for their mistakes. There are an infinite number of ways in which a person can ruin their lives within the space of a minute, sending money to the wrong address is just one more of them.