I'm not sure that I fully understand your question.
There was a confirmed 18 pound snakehead caught in Maryland this week. I cannot find a reputable source of a world record or biggest northern snakehead. I've been told that around 22 or 23 lbs is the world record, but I cannot back that up, it's just heresay.
As someone previously mentioned on this thread, when predatory fish (catfish, bass, striped bass, snakeheads, pike, musky, etc) get to the upper limits of their size, there is only one animal that can take them out....humans.
I also believe that it was already explained that while snakeheads don't have a natural predator (enemy) in the US, it is because they are not a natural species here. Predators do exist that are eating snakeheads (birds, bass, panfish etc) that's all been covered as well in the last few pages of posts.
What I was trying to ask was If you believe that 18pounds snakeheads are starting to become a common size for a snakehead in the US due to lack of predators. They are now not common at this size,but maybe in a decade?