It has become, functionally, a decentralized pyramid scheme.
Let's look at some of the criteria reviewed in the article.
- Investment Returns: Not Promised
The promise is peer to peer: players convince each other of investment returns and almost all players (that remain) are there because they believe in that promise. Once the last dude who wanted to buy pizza without giving Visa or Mastercard a cut has left the room...
- Open Source: The Opposite of Secrecy
Yes but that the mechanism of redistribution is (partially) in the open does not invalidate that something is a ponzi or a pyramid scheme. The openness is also partial, Bitcoin is still pseudonymous enough that we know what moves but not always who and why.
- No Pre-Mine
Early mining with exponential reduction in block reward is functionally equivalent to a pre-mine: the founder(s) have a considerable advantage. A bit more open but then one can also usually do well by buying early on the secondary market an explicitly premined coin that later becomes successful (e.g. ethereum). It's effectively a more elegant way to do a premine with nice deniability (harder to get caught for doing a security offering).
- Leaderless Growth
Yes it's decentralized. A decentralized pyramid scheme remains a pyramid scheme. It's not an intrinsic property of the tech but of the social happenings around it. (Many altcoins that are other instances of the same code have failed to get traction and become pyramid schemes.)