However so far it's not proving to be a currency (short term stability, long term deprecation or preservation) but only an asset class (short term instability, long term preservation).

So far it is only proving that it cannot be both.

For assets, one can choose to invest in already existing inflation resistant assets, and many investors and even unsophisticated laypeople did that across the ages before Bitcoin was invented. So essentially federally-issued inflationary currency is not really a problem of investment because there are other alternatives to it when investment is concerned.