Saying that investing in bonds, etc. is the "worst" investment is an exaggeration. If you compare mining bonds to USD-based investments, they look very good. Even though their values in BTC have dropped by half, their values in USD have still gone up. Add in the dividends and you are doing well.
Again: USD-based accounting is completely irrelevant. We are discussing BTC investments here. You're basically arguing that since the Zimbabwe dollar went from 1k per USD to 1bn per USD this means that some used car you bought made you a lot of money during the time it was slowly rusting in your front alley.
Well, 99% of the transactions I make are in USD, so it is relevant in the end. I prefer to stay in one currency or another, but I can't ignore the exchange rate if I have to exchange.
Also, I think you made a mistake with your Zimbabwe dollar analogy. Simply replace "Zimbabwe dollar" with "bitcoin". The car is worth the same in USD, but is now worth billions in bitcoins/Zimbabwe dollars. In your example, which is more relevant, USD or bitcoin/Zimbabwe dollar?