It would only be a ponzi scheme if the bank was originally setup to take deposits, with no intention of ever returning them, or ever paying interest on them as advertised.

But that's exactly what a BANK does.

You accrue interest on paper, but the bank never has enough capital to cover that paper.

A few people can get out ahead (just like a casino, even Bernie Madoff had a few customers that withdrew huge profits), and by doing so "prove" that "the system works", but just like a casino, they eat you up with fees, and they'll even hold your funds if you try to withdraw any amount greater than a couple thousand bucks (the "Bank Secrecy Act" makes this even worse).

That's actually one of the most attractive aspects of steem (and crypto generally), namely that I can send tokens of value to whomever I wish, whenever I wish.

Notes on the Bank Secrecy Act,

It has been amended several times, including provisions in Title III of the USA PATRIOT Act, which amended the BSA to require financial institutions to establish anti-money-laundering programs by establishing internal policies, procedures, and controls, designating compliance officers, providing ongoing employee training, and testing their programs through independent audits.[4] WIKI