1) Large amounts of new money are (currently) required to sustain today's price, and many more new "bagholders" are needed to create a large gain in price.
That is the same for precious metals and the stock market.
In fact, Satoshi said that bitcoin is designed like the fundamentals of gold.
2) Once you are "converted" many people are motivated to spread the word, and pleased when they get others to join.
That is the same as all things such as politics, religion, video games, social clubs, time-shares, protests, charities, etc.
Those are not considered to be ponzis.
3) The first people in made/make a HUGE RETURN on their initial investment. ....
That is the same as early tech stocks (microsoft, apple) and early pharma stocks.
All forms of speculation is based on buying now at cheaper price, to sell later in hopes of higher.
4) Sceptics and naysayers use the term "bagholder" to describe dedicated believers.
The term "bagholder" used today, originates from financial market trading, such as stocks.
The term can be attributed to anyone or anything by anyone for purposes to discredit, whether valid or not.
Conclusion:
By this logic, Bitcoin/bitcoin is as much as a ponzi as everything else man has created or attempts to control.
This could potentially include life itself, since the children born today are the bagholders of their parents.
So ultimately, it is worthless to go down this path. Your whole life is a ponzi, by your premise.