Even if there aren't any exceptions, you've successfully excluded everyone who claims (truthfully or untruthfully) to be even a little transparent, which almost all do.
I don't think I did that. I certainly didn't intend to. Perhaps it was a case where there was bogus transparency -- transparency that leads to complete opacity. For example, a bond that "transparently passes all money through to Pirate" is bogus transparency.
Also how do you measure suspicious returns? I remember my bank offering more than 100% "overnight" interest for extended periods, even when the inflation rate wasn't as high as Bitcoin's.
Suspicious would be, order of magnitude, more than double what you would expect from most completely transparent investments offering about the same level of risk.
So in summary, when you say that a well known person who gives a guarantee for deposits, who is limiting the total deposits to an amount that's not worth stealing, and who is mostly transparent with his investments is a Ponzi scheme because he's paying out interest more than banks do (but well within range of what can be done in the market), the argument seems to me to lose credibility.
I agree. I hope I didn't say that.