I would disagree on this last proposal. "The powerful getting more powerful" is a fatal design-flaw in the site, everything needs to be done in order to restore more balance.
Another probably better option: Make the first 2 flags do not count.
It would help discover plagiarism faster than a shield mode, and zero the rewards more effectively at the moment multiple people would flag.
A the 3rd flag, all the flags (incl. 1 and 2) kick in and the post is put down.
So all they'd have to do is make 3 accounts then right? :)
It has to be something more difficult, but easy for most people to achieve with some positive participation on the platform.