Well, the bitcoin market system is indeed a pyramid scheme. And bitcoin can't be a bubble, but the nature of the market can consist of constant bubble growing and bursting. It would be an Ponzi scheme if it would turn out that most markets are presenting falsified market data and the amount of fiat that is allegedly flowing into markets is not true.
The thing that makes bitcoin attractive to most, is the same thing that would be the end of bitcoin - deflation. Looking at the community, it seems that over 90% of people who are interested in bitcoin, are so because they have hopes of buying low and selling high. Deflation is the thing that attracts people who dream of gaining wealth by just being in the right place at the right time. We mostly see the same people visiting motivational lectures and reading books from Robert Kiyosaki on how to find a shortcut in being a millionaire. These people dream that the bitcoin pyramid will grow bigger and bigger and bigger, because if it does, then the current bottom of the pyramid will be the top in the future.
But the problem is that in an economical perspective, money shouldn't be considered mainly as value. Money should be the intermediate tool to help trade value, not be value by itself. If money is attractive as an investment opportunity then it is very attractive to speculation and that leads to hoarding. And that creates very big problems with price stability, and more importantly with wealth distribution. The rule applies that the more bitcoins you have, the easier it is to gain new bitcoins with market trading. The ones that have hoarded the most can actually know the future price because they have the means to  create the future price. That will lead into a snowball effect where the richest become even richer everyday and the bitcoin based economy would suffer bigger wealth distribution issues then fiat ever had. Inflation is still the key because money should be unattractive to hoard and should only be used as a tool in trading.
I think that most of the bitcoin community is ok with bitcoin deflative nature, because that would make them a lot richer then the 99,99% of humanity. That is the greed that drives the bitcoin community where everyone wants to be a lot richer then others and want to be so without actually doing any real work that would have any practical value. That is why the bitcoin market is indeed an pyramid scheme under the guise of technology. And the entire pyramid will fall at the critical point when there won't be any new people wanting to become the bottom of the pyramid with hopes of rising higher in the future. When the inflow of new people, who would rise the old people, will stop, then everyone wants out and it will be a total crash. I personally don't think that bitcoin will live long enough to meet this critical point of final crash. It is more probable that in a year or two, another crypto will surface, that will outmatch bitcoin in general quality and then most of the value from bitcoin will flow into this new coin.