If you’re reading someone else’s article, then it’s important to know whether you’re dealing with a sampling bias when looking at the arguments (more on this later). But my main point was about the evidence we should derive from our own conclusions, not about a Fully General Counterargument you could use to devalue someone else’s arguments. If you are paid to cleverly argue, then it is indeed a clever argument to say, “My opponent is only arguing cleverly, so I will discount it.”
However, it is important to try to determine whether someone is a clever arguer or a curious inquirer when they are trying to convince you of something. i.e. if you were in the diamond box scenario you should conclude (all other things being roughly equal) the curious inquirer’s conclusion to be more likely to be true than the clever arguer’s. It doesn’t really matter whether the source is internal or external. As long as you’re making the right determination. Basically, if you’re going to think about whether or not someone is being a clever arguer or a curious inquirer, you have to be a curious inquirer about getting that information, not trying to cleverly make a Fully General Counterargument.