Do they even know what Ponzi scheme really mean? I doubt :-)
On steemit, we aren't paying any upfront fees, we aren't luring people to join under us, we aren't earning any referral stuff. How it could be a Ponzi scheme? If I have 50 STEEM in my account then I can transfer it to any exchange, convert it to BTC, sell that BTC and get hard CASH in my pocket! People this days man....
Regarding TBC being scam, you have already answered that in another comment 👍