Whatever the motives behind the Bitcoin's development, it still cannot be consumed by nobody in its circulation chain. Meaning, profit or benefit for investors, criminal or not, can be obtained only by using funds from new investors. Hence, Ponzi scheme.
It is definitely NOT a Ponzi scheme. In a Ponzi scheme early investors make money off of newly injected money into the system. With bitcoin, criminals make money by using an uncontrolled unregulated transfer of value system or con men use various schemes to convince people to send them their money using an unregulated irreversible currency.
Well, criminals are just people who have committed a crime and as such they are not immune to Ponzi schemes. A Ponzis scheme is NOT when early investors make money off of newly injected money into the system, because every investment fits that definition. For e.g. if you had put 1000 USD into Apple stock at the beginning of the year, and sold it today, you, as an early investor, would have made money off of newly injected money into the system - which is injected by new investor, the buyer of your stocks. So, is Apple a Ponzi? No. A Ponzis scheme is when investors put in consumable resources - resources with the capacity to be used, consumed or practically utilized by end consumers for satisfying their needs, and end up with non-consumable item which has no end consumers and as such it cannot be used by anyone. For e.g. a car is used by end consumers for driving, a dollar for settling loan obligations, food for providing nutritional support, a raw material for producing finished products etc. Hence, investing into dollar, car or food industry, crude oil, etc., is a not a Ponzi scheme because funds are transfered into something that is used for satisfying actual human needs, and these needs are the very reason why economic activity that produces and trade consumable resources exists. But, when funds are transfered into bitcoin - a number associated with an address, this is a Ponzi scheme because this number cannot be used for satisfying actual human needs. Instead, it can only be transferred from hand-to-hand, from member-to-member, from address-to-address. If an owner of this address is criminal, nothing changed - Bitcoin is still a non-consumable item and thus, putting your funds into it is investment into a Ponzi scheme.