Are blockchains decentralized? Do exchanges rule the stake governed blockchains?

Exchanges hold a substantial amount of tokens from each blockchain. An interesting case just happened. They have just used their stake to take control over the Steem blockchain.

Governance on some blockchains are based on stake, this applies to both Proof of Stake (PoS) blockchains like Gridcoin and Delegated Proof of Stake (DPoS) like Steem.

The unprecedented event happened and several exchanges allowed to take control over the Steem. It will be interesting to watch the industry reactions. What are your thoughts?