many knows much about steem and steem technology, just a brief back ground and I will jump into the issue

steem

steem platfrom solves the problem of where publishers and content creators are monetized for contributing to the social network/content.

Content generators has to engage affiliate marketers and advertisers to generate any income,these middlemen-enabled solution only help a few, and the most popular and rich gets even richer.The content creator has to fit the advertisers needs to get any traction which impact the integrity of a creator’s work

So steem took the power of decentralization and block chain to solve this and has been successful so far even though scaling and retention are still a problem.

Consensus Mechanism

Steemit is built on a delegated proof-of-stake consensus mechanism, DPoS used in bit shares and EOS
The idea is more democratized version, people elect witness nodes and they run the network and regular folks do not need to spend any money to use the network. Besides this approach make it more scalable and fast!!!! Not everyone needs specialized hardware or software. This is perfect for decentralized networking solutiona decentralized youtube,fb, twitter and so on

In each round 21 witness are selected to generate block, 20 who are in the top list selected by the community and 1 time shared from the rest. The assumption is that if one of the witness censor or malpractice, he can be voted out by the community. In reality the whole steem network is done by the 21 witness, this indeed is centralized.

Hijacking the network

When steem have millions of users, why wouldn't a company itself is setup to hold top 20 witness. This could be hidden and can take their own agenda ? 20 seems too small and seemingly vulnerable to manipulation

Biased advantage

Once you are in top 20 witness, you can stay in power, because you have incumbent advantage , more people know you, more revenue generation to market yourself and promote your agenda.It will be very hard for another witness to move to the top spot.

Term Limits

Once steem reach more wider audience then possible witness should have term limits , may be for few months and allow others in the list to move up. This kind of rotation makes it more democratic and make sure it truly stays decentralized