This was nothing like a Ponzi scheme - the money was lost due to bad trades, poor collateral, bad accounting/compliance with probably a little bit of criminality thrown in at the end.
Although they were trading crypto it was more like an old fashioned/real money collapse.
There's a slide deck floating around[1] purported to be from Alameda research in 2018. That deck claims they offer 15% fixed returns to investors. If that slide deck is genuine, it seems possible that the unaccounted for money at Alameda Research went to paying for redemptions by early investors. Given how bad the accounting at FTX/Alameda seems to be, it seems possible to me that Alameda investors were paid back at high APYs even as the underlying strategies performed poorly, and the people at the top might not be aware that they were heading towards insolvency. If this is the case, it would be close to a pure Ponzi.
Now I don't really know how likely this is because there's very little public information about Alameda. It's also possible that Alameda bought Doge and Shiba which proceeded to crash 10x.
On that reasoning any company that is successful and people make profit early on then fails would be a Ponzi. It still looks like Alameda/FTX was initially profitable and then began to make losses which resulted in FTX customers (not investors in Alameda) deposits being loaned/stolen.
An investment fund which is successful early on then is not successful but still pays investors high returns is a Ponzi in my opinion. Many Ponzis in history have been backed by a legitimate business.
Although they were trading crypto it was more like an old fashioned/real money collapse.