The problem is a sanely run conventional currency is sanely run until it's not. For EUR, USD, etc., that could be a very long time, but at some point, they may

The problem is a sanely run conventional currency is sanely run until it's not. For EUR, USD, etc., that could be a very long time, but at some point, they may face the same structural forces that causes other currencies to overly inflate, e.g., economic conditions change, political winds change, and suddenly you have elected leaders making disastrous choices. Your solution is akin to saying that dictatorship is the best form of government, just make sure the dictator is a good and competent person! This is true, but ignores the precise issue, which is that you can never actually assure the critical qualifier. By contrast, BTC, with an algorithmically determined monetary policy, does actually solve the issue. And the other issues that you raise, i.e. that a highly volatile asset is a poor unit of account, are not actually issues -- you can simply transact in USD (or a stablecoin) for most day to day matters, while having the ability to always revert to BTC or other assets as an uninflatable store of wealth when desired.