The one thing I'd add to @andrachy's answer here is that in reference to the Sybil attack it's basically the same as on Bitcoin. You have to actually produce blocks in order to have governance votes. 1 block produced is 1 vote (it is not stake weighted). In order to produce more blocks than anyone else you have to first acquire stake and burn it and then actually produce blocks for quite some time to get your governance votes in. Changes to governance require 70% of produced blocks to be voting for a proposal, non-governance changes require 60%. This is very similar to Bitcoin because in order to attack the network there you would need to acquire 51% of the hash power and then actually continue to produce blocks - you couldn't just stop producing, you'd have to keep "owning" the network in perpetuity. This is part of why I say PoB is more similar to PoW than PoS. In addition, the default governance vote is "no" so it isn't possible for someone to sneak in a proposal without block producers actively engaging.