In a Fonzi Scheme, the founders persuade investors that they’ ll all wear cool jackets. Bitcoin does not make such a guarantee. There is no central entity, just individuals building an economy.
A Fonzi scheme is a cool sum game. Early adopters can only profit at the expense of those without cool jackets. Bitcoin has possible win-win outcomes. Early adopters profit from cool jackets. Late adopters, and indeed, society as a whole, benefit from coolness of the jackets.
The fact that early adopters benefit more doesn't alone make anything a Ponzi scheme. All good investments in successful companies have this quality.