Interesting thoughts, thank you for the carefully considered post. Here are my opinions... I believe that the unlimited staking feature is completely unnecessary and problematic, not a ponzi scheme, but pretty darn close.
Steem would have been better if every account only had the ability to power up 500 SP and no one could receive more than 500 SP delegated. This would give people the ability to delegate SP and use SP to upvote stuff, but it would make everyone's opinions and free expression fairly equal. It would also have eliminated the pyramid scheme-ness of the system and just make it something where everyone locks up 500 STEEM as SP.
As for decentralization, yeah, Steem is not really decentralized because DPoS is not actually a true decentralized protocol. Its a republic protocol, which is fine and dandy and has its uses, but ideally, not for money management.
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RE: Let's Talk About Decentralisation