While you could argue that a startup and a ponzi scheme can be considered similar because they both benefit earlier investors/members more than later ones, I'd argue that they are fundamentally different due to both the intention and the method - (i) the intention of a startup is extrinsic, i.e. it is to provide a real product or service based on a genuine or perceived customer need, while the intention of a ponzi scheme is intrinsic, i.e. it is solely a money making scheme with no product or service outside of the scheme, and (ii) the method of the startup is such that it will typically try to benefit most or all investors and customers to a greater or lesser degree, while the method of a ponzi scheme is such that it will benefit the earlier members at the expense of the later members (necessarily because nothing exists outside of the scheme).
Something that you can model as a collectible doesn't do this. No matter how many promises of revolution you attach, it's still a commodity where you can buy and sell units based on supply and demand, and everyone profits or loses based on where the price goes. And they're generally aimed at a perceived customer need, at least.
For an honest believer, the value of their coins remaining stable is fine, they just want to be able to purchase things easily with them and/or do smart contract stuff.
The word 'scam' is appropriate for some coins. The words 'ponzi' or 'pyramid' are very rarely appropriate.
On a side note, the smart contracts set up to do a ponzi were interesting. It turns it into straightforward gambling, without the risk of someone taking the money and running.