The wheels of all of this began turning in '71 when the US dollar, THE global currency, was no longer backed.
The use of BTC bears resemblance to Gresham's law. As far as other coins, all are securities and not commodities because more coins can be issued, unlike BTC. The $ has aspects of a security because the quantity of dollars may be diluted. So BTC is the better money than sheetcoins or fiat money.
Armstrong has a point about BTC volatility and store of value. However, all currencies, especially fiat, fluctuate in value. The $ has been an exception, certainly when it was backed in gold or when Breton Woods was in place. So Armstrong's comparison assumes an historical aberration.
As long as it can be traded for labor worldwide it is reserve currency. As Americans are in US denominated debt, and paying that every month is the driver for 50% of the US labor, the greenback is secure. That you owe a banker for the next 26.5 years makes him look out for your well being.
Biblical prophecy. One world currency. What do you think that is? Bitcoin.