They were a few middle-class techy hubristic kids who figured out how to game the crypto system years ago, via leverage and arbitrage opportunities, to make millions during crypto tradings early "easy pickings" years, on crypto platforms which would later be their direct industry competition.
They then transitioned to become part of the system themselves, as an Exchange ... while continuing to expose funds (their own, and their customers) to high risk-reward scenarios, again/still, on their competitors platforms. What else is there?? in the small pond that is the crypto-verse.
That degree, and unwise configuration, of exposure is what caused the collapse.
I don't believe that Ponzis central tenet - to sustain only via new entrants - was ever their long term business tactic. The fact that Alameda/FTX ended in the final flailing desperation of an extremely poorly piloted sinking ship was its own indictment, but that doesn't make them 'a Ponzi from the beginning'.