If you invest in Bitcoin, it has the highest probability that you will get profit in months or years of holding among the other cryptocurrencies.
It depends on when you buy Bitcoin. If you buy at the right time, then you will easily get profits from Bitcoin. We can hold for months or years, there is no problem how long to hold Bitcoin. As far as we know the cycle of bullish and bearish, we know when the right time to take profits.
But I wouldn't agree that you can make big profit and can turn poor people into rich. If you want to become rich invest in Alts.
Being rich isn't something easy. Even if you invest in altcoins, there is no guarantee to be rich. You even can be poor if you invest with all of your money but choosing the wrong altcoins. Be careful to choose altcoins, many of altcoins can turn to be dead coins. IMO, if we want to be rich, it is better to invest in Bitcoin with bigger money.
In terms of sustainability, I believe that Bitcoin is the number 1. Fortunately, people prefer sustainability than with high risk high rewards.
Of course, Bitcoin proves that it always increases from one cycle to another cycle. Bitcoin has strong fundamentals and Bitcoin price growth looks quite consistently. If we can hold Bitcoin for months or years, it is quite safe to invest in Bitcoin. Just don't hurry to take profits from Bitcoin!