There's a difference between Ponzi and actual DeFi projects. Stablefund turned scam after such a long period and it was heartbreaking but I won't say it was a ponzi or anywhere close to that. They just made some mistakes like compound deposits were not locked or something like that. Now there's Myst Finance who are doing everything SF did but are much more robust and transparent.

Always ask projects for proofs of profits before diving too deep, at least that's how I select where I invest.