Yes, you are right, one can invest in currencies by playing games with exchange rates. Drew_G’s point was comparing Bitcoin to dollars, where dollars are mostly stable (very mild inflation, though not actually enough IMO), while every example of instability you had offered was tied to the instability not of the dollar, but investments.
Bitcoin is treated in a fairly confused way as both currency and investment, which is part of its problem. It’s pretending to be a stable store of value for the purposes of being used as a means of exchange, with clever mechanisms to facilitate payment, and much cheerleading of it as a currency, but it’s also deflationary so by design it can’t work well for that purpose.
There are other cryptocurrencies that are much better designed, Bitcoin was an obvious dumb idea out of the gate since it had built in instability.
