You're under the assumption that Steemcleaners is acting in a manual fashion to perform this work. There's no possible way that is 100% true.
This is a bot with an algorithm that compares text with other text. Maybe the manual effort portion takes an hour a day?
Plagiarism is the easiest text comparison to spot and takes effectively no thought to write that code.
I agree that every user should actively look out for and report abuse of Steemit. Otherwise you're (metaphorically) setting Steemit up for failure.
We are acting in a manual fashion... it is literally just a group of people (myself included) who spend the time manually going through posts, logging them, and commenting. Yes, cheetah is a bot, but look at all the posts that cheetah didn't catch that are still caught and logged as plagiarism. There is no bot for photo plagiarism, google translated crap, spun articles, etc...