But when you see websites saying "Pay for stuff here using BTC", it is clear that they are trying to make BTC into a currency.
Those who wish to use BTC as a currency are discouraged from doing so, as long as this stupid hyper-deflation is occurring. No one wants to spend BTC on anything anymore.
It is a currency. It satisfies the Coincidence of Wants, it is used as a means of exchange, that makes it a currency. Cigarettes have been used as a currency (in WW2 concentration camps, prison, times of famine or war etc.). But nobody suggested cigarettes or tobacco be the thing we pegged our national currencies on, its just a thing that represented value that people traded for goods and services. That's a currency, not a national currency though (because as you mentioned earlier, that's probably a bad idea which we know from history with gold).