I think you are right in a way. If we are not strict with the definition of a Ponzi scheme, a lot of things can be classified as Ponzi.
People who call Steem a Ponzi are in fact implying that stocks and other crypto-currencies (including Bitcoin) are also Ponzi. Which obviously does not make sense.
When you buy a stock in company (or a Bitcoin token), you do it because you assume that in the future there will be someone else who will buy it from you at a higher price. So yes, the financial outcome of your current investment depends on someone else making a new investment in the future. If we treat this as a valid symptom of a Ponzi scheme (which is wrong!) then yes, most financial instruments (Steem included) are Ponzi schemes.
Agreed. Or if we were in a brokerage industry and didn't want to get into legal trouble we'd simply point out they are 'speculative investments'. Same difference.