It's obvious that bitcoin is a ponzi.

Ponzi still exist nowadays because of bitcoin, so it means that bitcoin is not a ponzi. There's a lot of new platforms spreading all over the social media that uses cryptocurrency just to attract many users in their ponzi platform. A ponzi is a pyramiding scheme, a business platform where the money you earned is from the other people who put initial investments. There's no referral bonus gained to those who recommends bitcoin to the other people. And there's no specific amount needed for you to invest in bitcoin, even a 1$ can make you money but don't expect too much.