Having a product or something like that is a significant difference. Speaking of bitcoin, it is difficult to draw any conclusions. Not so simple.
But definitely, can't be considered as a financial pyramid by definition. You can invest anytime you what, and you don't need to market it by any sense. And its up to you how much money you going to put up. And no single person is benefiting if you are going to trade (buy/sell). The appropriate term should be "investment portfolio", in my opinion. Because the moment you buy, you hold that assets, which in this case bitcoin. And you have total control of it + privatekey in your wallet.
Exactly, there's always a way out. And it won't collapse under your feet when you're least expecting it. Maybe some Altcoins could be considered as ponzi/pyramid schemes because the owners just pull out their investment when the little people like you and I are least expecting it. Telegram groups close, exchanges reject the coin, people just disappear into thin air. That, by definition is a pyramid scheme. Bitcoin is just an investment opportunity for your portfolio, and a good one at that.