Yes that's the paradox here :

A ponzi is a pyramidal system used to scam people but in order to scam people you must not tell them how the ponzi work and of course you won't tell it is a ponzi.
Here you know exactly how it work and the transactions are transparent.
So it is a "legit" ponzi.

You can definitely make money but it will come one day where someone will send a big amount of BTC that he'll never get back because no one will send as much BTC as him.