Risk is a question of perception and risk as a number doesnt make any sense. If you say: bitcoin had higher returns or increase of price" okay thats one thing but "Bitcoin has far higher risk-return ratio than most [...] assets" is not really true because the risk is unknown or percieved and valuated differently... depending how you evaluate the risk its a complete different thing. Crude Oil could be risky because OPEC is a fucked up cartell and should be stopped but do you multiply the returns then by 0.1 or 0.01 how is the chance Greta Thunberg stops this? The risk of bitcoin is the highest in any asset because its a macroeconomical experiment so the multiplier should go to ∞. Then the returns in real numbers go to 0. imho
Even though I believe in this experiment! And I like my real $$$ returns this graph is nonsense. In german there's a saying: "Don't believe in any graph you haven't faked yourself" it applies here pretty well.