Not a narrative from bitcoin white paper, but from analysts (I am myself analyst) and people generally. On white paper, bitcoin has limited supply. The limited supply makes it deflationary and a possible means of hedge against fiat as its devaluation is not persistent but followed with uptrend and possibly all-time-high.

About gold, it suffered price reduction in some years, but still attaining all-time-high. According to what I have read, gold price valuation since 1980 has been actually from fiat depreciation. If true, this is how highly depreciative fiat can be. Fiat devaluation is even worse in developing and underdeveloped countries.

It is about what people has been seeing happening that got them into conclusion. I still see bitcoin to attain highrarketcap, and that aside, fiat is so inflationary over long term.