You say let the community come together to deal with but there have been years of evidence that has shown that individual people (for the most part) don't go hunting for plagiarized posts for several reasons.
It isn't in their monetary interest to do so. Why waste the time and effort (or voting power if you choose to flag). Few people are that altruistic to do it out of the kindness of their hearts and if this platform have proven anything its that people need to be incentivized to act.
Small groups/individual actors face retribution if they attempt to flag something, even if a post is blatantly plagiarized are you going to risk your accounts reputation to deal with it?
Lastly, this is the community coming together to fight it. Even without any delegation from Ned the SC account still has a ton of SP. Steemcleaners doesn't work for steemit, they are a group of people who believe fighting the abuse on steemit is worth it. Like you said, its a decentralized social network, you can't stop like minded people from joining together for a cause they believe in.
It is exactly accounts like @steemcleaners that create this problem. By posturing as the solution, other users leave the problem to them. This same dynamic has created a vast increase in criminality in the US. Prior to the turn of the 20th Century, there were few police in the USA, and much less crime - because people knew they needed to provide their security personally.
Armed civilians can prevent crime. Police cannot, but only play historian after the crime has been committed. In this way police actually cause crime to increase, because ordinary civilians leave their security to the police, and police cannot prevent crime.
Absent @steemcleaners, ordinary users would have to police Steem themselves, and the possibility of being individually targeted in retaliation by abusers would have been resolved, easily.