The problem with using it as either a gamble or an investment is that the person/people holding control over the currency are doing so with the intent to make money. More often than not your money is gone the instant you pay in if they decide to make it hard/impossible to cash out. This is what Logan Paul's scam crypto ended up doing. Say what you will about the US dollar, their main incentive is to stay in power which backs up the legitimacy of the currency. They're not just going to rugpull the dollar because it would run counter to that goal.

It's fundamentally impossible for crypto to fulfil that role because everyone involved is just there to make a quick buck.