"There is no need to introduce mechanism for coordinated downvoting..."
That's what saved Hive from bidbots - even though there are still bidbots operating on Hive, they don't just overwhelm the inflation issuance anymore.
"They are also used to trim rewards that downvoter finds excessive..."
You mean maintain the control of governance the oligarchy possesses. Taxation is theft. It's also tyranny in a plutocracy, which is what Hive is.