Survivors through crashes will have chance to become crypto made millionaires or even billionaires if they can survive and own some amount of bitcoin or good altcoins after crashes, dont' lose all their money.
Altcoins even have the tendency of given more than 100%, I dont know of the altcoins we have as of now, but the altcoins that I know which I held some before the last bull run of 2017/2018 had their value even shoot up as high as 1500% at some poin.
It's important to keep mainly investing in good altcoins.
So, altcoins are what you can invest with little capital and become a millionaire through it like you said, but we still have to invest in very good altcoins that have the chance of increasing that way with good products, otherwise, we will end up wasting our time with these shitcoins believing they will rise.
It's low probability if it is not impossible.
Therefore, the chances to become a millionaire are so slight that we can simply forget about them. Nevertheless, you will earn much (not a million, sure) if you continue working with cryptocurrencies and do not quit it.