Well, losing money and being a "victim" in a ponzi scheme are not the same thing. Of course, everybody investing somewhere should understand the risk. But with your argumentation, there is nothing like a ponzi scheme because of exactly that - they should understand it first.
Obviously, presenting guarantees for a certain ROI indeed are a strong indicator for a ponzi scheme, and this is exactly what has been done here. Nobody from the Bitcoin core team has ever promised any kind of return, and that is the difference.
People now losing money because the system itself wasn't sustainable and had to shut down again is a strong sign for BitConnect being a ponzi scheme.
I do not believe there was a guarantee on the percentage of gains. I do believe the average was about 1% return, but this could have also been 2% or 0%. How is this different from a bank offering 1% return on your savings account? The principle is the same, but in the case of a volatile market extra gains are/were possible.
The reason why the system would end up failing is because of the reinvesting for compound interest. However, I do not believe it would ever get to that point in any reasonable amount of time. The amount of money it would take for 100,000 users to reach $100,000 of daily payout is insane. Plus, the discipline to not pay yourself to get to that level seems extremely unlikely.
The traditional ponzi scheme and definition is new investors pay old investors. In the case of BitConnect their business model was paid on the increasing price of the Bitcoin used to purchase their token and then the price increase of their token when lended to the company. Since the company controlled the majority of tokens and could inflate the price of their token, and then return investors a much reduced amount of tokens back after capital release, I would argue that new investors did not pay old investors. Furthermore, this business model would be able to continue indefinitely making the business and investors profit if it eliminates the ability to reinvest after a certain amount of money.
I know this stance is not normal and many people will shout that it is a ponzi scheme, but I think they are wrong. You could maybe argue that this is a different version of some business model that could create some FUD that it is a scam, but it is definitely not a ponzi scheme.