The most obvious flaw in the logic that it is unsustainable is the implied assumption that this 20% yield is static and can't be changed. Witnesses can lower it to 0% if they wanted to in an instant. It's a dynamic variable that improves monetary elasticity and stability.

If Hive spikes x10 because everyone is buying HBD and burning Hive and increasing the debt ratio and creating massive leveraged risk... then yeah... lower the yield because it's unsustainable. What we are seeing right now is the opposite of that. The 20% yield gets better and better as the price of Hive crashes. Don't even need to consider lowering it while debt ratio is below 5%.