Bitcoin is a Ponzi scheme.
Its value may be determined according to the greater fool theory but it's definitely not a Ponzi scheme
Well, that actually depends on your point of view
If we assume that the defining criterion of a Ponzi scheme is paying profits to earlier investors with the funds obtained from more recent investors (as
per Wikipedia, no plagiarism intended), Bitcoin fits this definition pretty well, at least as far as its speculative part is concerned (which is the best part of it anyway).
A Ponzi scheme is an actual investment scheme. It promises returns on investment (which Bitcoin does not) and requires that the operator collect investments and dispense profits.
You're basically just describing the activity of speculation. Under your definition, gold and fine art seem like they would be Ponzi schemes too.
You can only earn dough by buying coins at a lower price and then dumping them on someone else at a higher price
That's literally what
the greater fool theory means, and it applies to all assets, not just BTC. Ponzi schemes are much more specific.