You are quite right, if not for any other reason, then the fact that the existing blockchain infrastructure lacks the scalability that would make it the default currency of the future and additionally, the fact that the prices are so unstable doesn't help it's case at all, the perfect Cryptocurrencies for worldwide adoption has not been invented yet but you have to consider that the first computer invented didn't give the best access to the internet, the more it is worked on, the more it keeps improving.