We should think more about the risk of having all your investments in one single portfolio, such as bitcoin.
well , it has been said already that it is better to invest in single coin such bitcoin than currency that represent altcoins because those are very risky and most of those died in sooner time.
so it is better for the said single investment than other coin to Bitcoin.
Bitcoin happens to be the most reliable cryptocurrency for investment but at the same time, Bitcoin is a highly volatile asset. So I will still advise you to diversify your portfolio into multiple sources.
all currency are volatile mate ,except from Stable coins so yes either diversifying or not? yet cryptocurrency are volatile and you will only learn when you experiences losses before gaining.