PS: there is not a right or wrong here, there are two different things being talked about and you are trying to combine them under a blanket statement.
This is absolutely correct.
The abs have a very limited ROM when it comes to direct abdominal training, so between the squats, deads, OHP, and rows your are pretty much putting a load on the entire range of motion. Not to say that direct abdominal work is useless, I perform it myself, but saying that the function they play during heavy compound movements won't strengthen them is not true.
Now I am not writing this for the sake of an argument or to necessarily change Metabolic's mind, it's because someone might come across this thread and I want them to see the entire picture.