That said, Bargue's process was intended for communicating good taste to 'lesser' commercial and decorative artists as much as it was used for training fine artists. It's a method that essentially boils down to copying pictures of sculptures which are twice removed from nature.
Before and since Bargue, we've had great artists who gained their chops by being students of nature. Many of them never saw a Bargue plate. Many of them didn't use the sight-size method. And there were a lot of skilled Bargue disciples who never had any real impact on art history.
All that to say, I don't think the parent comment is at all out of line. Copying Bargue plates is a fine warm-up or substitute for life drawing, but it's neither necessary nor sufficient to becoming a great realist (we had those long before Bargue). Plus, the world has churned out countless nobodies skilled in the art of copying Bargue plates (which I say as someone who would like to be one of those countless nobodies). It's just not as important as people think.