What?! it is a valid engineering criticism. I am not sure I have a rack that is not triangulated - I seem to bypass those that are not. You seem to be dismissing the history of frame construction (scaffolding, Eiffel Tower, bridges) and these days even of molecular design.
First off, I said it is not a perfect triangle. Many racks are not. Many have adjustable rods to connect to the chain stays that look a lot like Pinigis's. When I first read your comment, I did not know which plane of the rack you meant. I think it likely that you're letting the perfect be the enemy of the good.
BTW, I did not mean to criticize you. I very much respect you and your opinions. I just wanted to understand your comment.