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.
....
I am a retired engineer, and have lots of miles of bike touring with heavy loads on a bike. It is my professional engineering opinion that sometimes all you need is a light duty rack.
I usually tour with a Tubus Logo EVO rear rack on my medium or heavy duty touring bike, extremely stiff and robust. On my light duty touring bike I tour with a Racktime Addit rack, also very stiff and a weight capacity that although is less than the Logo is still more than adequate for my needs.
But both of those racks are in storage right now because for riding around near home I am looking for a wider platform and do not need the weight capacity of those touring capable racks.
Two photos of part of my light duty touring bike, the first photo is with the Racktime Addit rack that I use for loaded touring with my camping gear.
Second photo, this is the rack I use for riding around home. It serves my needs very well for that purpose. Occasionally used with one or two shopping panniers, but often just used with a rack top bag, it is more than adequate.
The prototype rack cited above on the folding bike might not be built for heavy duty touring, but perhaps it is sufficient for most needs of potential customers?