I would not go as far to say that bitcoin is a gamble but it can't be a magic fix to whatever the issues are in fiat. The thing is fiat's issues are its own alone. Bitcoin is not meant to replace fiat. But it can serve as an alternative. Right now, since bitcoin is not massively adapted by everyone and every country yet it makes it harder to completely make use of bitcoin and use it to its maximum.
Now fiat is still needed no matter how you do not like fiat, it is almost impossible to live normally without some fiat on you. I would like to see someone live with just bitcoin. So no it is not a magic fix but I believe that bitcoin has been reliable and stable enough to not be called a gamble.
As you said, bitcoin is not yet massively adapted by everyone and every country. That shows that it has not really escaped the potential risks and become safer than other traditional assets, so there is nothing wrong in saying that investing in it is nothing more than a gamble. A gamble can bring us big profits but also comes with high risks.
This may change in the future but for now, given bitcoin's popularity, legitimacy, and relative youth, it's clear that investing/holding bitcoin is more of a gamble.
By the way, people always compare bitcoin to fiat and claim that bitcoin is the better solution. But as I see it, people only use bitcoin for speculation and when they have enough profit, they will go back to fiat and traditional assets. This makes me wonder, do people really see bitcoin as an alternative or are they just taking advantage it and will leave it once they have achieved their goals?