When Is a Blockchain no Longer a Blockchain?

Some commentary on the latest Steem Hard Fork. I don't get into how this hard fork stole funds from over 60 user accounts, transferred them to a single account which later got taken over and transferred those funds to the Bittrex exchange. Plenty of people online already talking about that. Instead, I wanted to ask a more fundamental question as to when a blockchain is no longer a blockchain. How do we view distributed consensus and at what point does it just become a centrally controlled database without any real security?

Here's the tweet thread I referenced: https://twitter.com/lukestokes/status/1263438444510003201

Here's the backstory: https://peakd.com/steem/@lukestokes/how-steem-became-hive

Here's the original open letter from Justin Sun after the very first action taken by the Steem witnesses almost three months ago: https://steemit.com/steemit/@justinsunsteemit/open-letter-to-steem-community