I don't want to get into the debate on the definition of a pyramid scheme, but what was anyone risking by mining bitcoins for essentially nothing in 2009-2010?
Of course, many of the early adopters got very lucky while taking almost no risk. This happens with gold and oil too. However, those that chose to hodl started taking real risks as soon as Bitcoin hit 1$. Bitcoin hodlers today are obviously taking substantial risk as the price could drop massively at any moment.