I don't know if there is any system created by Steemit to detect such things, but I guess there are some bots created by users to track such activities. The only punishment one could get for such behavior would be flags from other users if they seem entitled to take action towards such things.
I think one of the biggest shortcomings is that this situation can not be controlled. I usually hear them ignoring their large accounts I'm not here to test more. If there is such a situation, the platform has entered a troubled path. No system of weakness crushes weaknesses.