New money needs to come in daily in order to sustain the price as new steem is created every single day. In that regard it's a ponzi regardless any voting behavior in my view. I don't see it as a ponzi scam as everything is very open and transparant though.
The main issue I see right now is that payouts in general are just way to high not to be abused. 9.5% yearly inflation + SBD at 6.7x the price they were intended to be.
Every currency and asset requires continued buying pressure to prevent its price from collapsing. Does that mean gold is a scam because it keeps being mined and if people stopped buying it then its price would collapse? The value comes from the consensus of a market of people believing that it's useful/desirable, and preserving that consensus depends on the asset actually facilitating sustainable productivity.
I agree there should be some technical updates to the system to reduce abuse, but getting support for those will take time and without educating the voters they won't be enough to save it anyway.