But isn't the exact problem you are talking about? Not enough people are using their upvotes to help the platform and content. Why would anyone believe there would be enough people using downvotes to help content and the platform?
The reason you have "never come across a scenario where well known/well established content curators/curation movements get flagged" is because it takes money out of the pockets of the self centered people in order to flag. They can choose to vote themselves or they can choose to flag. Not both. Unless of course you give them a separate pool of flags that does not hurt their earning power.
And is it really the established content creators who need protection or is it new people starting out who could possible bring great value but they never get a chance?
Right now the self centered people have a way to help themselves and indirectly hurt others. A separate pool gives them a way to help themselves, indirectly hurt others and directly hurt others.
You are correct that it is impossible to tell unless you try. It might work. But then again monkeys might fly out of my butt.