This is a gamble in the same way leaving your wallet on the bus and hoping to come back, find it and also have another $100 stuffed in it.
This is not a gamble in the form of a casino game, a wager or a bet.
This is a scam, a grift and most of all a tax on the gullible.
I don't think that's fair.
If someone runs a Ponzi and claims they are making profits by mining, day-trading, robbing old ladies of their pension, or whatever else then that's a scam. Investors think they're making money in one way and it turns out they're being paid only from new deposits. One day it all stops and investors are surprised to find that they are out of pocket.
One the other hand, if a Ponzi is advertised as a Ponzi where the operator is up front about how it runs, and warns that payments will pause if new deposits dry up then everyone knows what they are getting into.
"scam" is defined as "a dishonest scheme; a fraud". This doesn't fit that definition. There's nothing dishonest about it.
"grift" is defined as "a petty swindle"; "swindle" as "a fraudulent scheme or action", and "fraudulent" as "obtained, done by, or involving deception, especially criminal deception". Again, there's no deception here. Everything is out in the open. Deception; deceit, deceitfulness, duplicity, double-dealing, fraud, cheating, trickery, chicanery, deviousness, slyness, wiliness, guile, bluff, lying, pretense, treachery. There's none of that stuff.
Leaving negative trust feedback for someone running such a scheme doesn't seem appropriate to me.
Edit: Your trust feedback says:
Gambling that a ponzi operator will not run off with your funds IS NOT a gambling game.
That isn't the game. Every gambling site you play has a risk that the operator will run off with the funds, the same with every other service you entrust with your coins such as exchanges.
The game is whether you think the Ponzi will survive long enough for you to get paid back in full.
Edit2: also, you wrote that you risked "21,000.00000000" BTC with this guy. That's clearly not true, and is an abuse of the trust system. You are on the DefaultTrust list and so have a duty to use that power responsibly.