Much heavier solution. Their backpack looks like it weights more empty than my backpack + items in it, which would be 2.25kg. And they need a rack.
"but someone must have told them this would put too much strain on the seat post and crack the frame." That's an interesting point, do they actually say that at some point or is that an assumption?
Sorry if I sound a bit presumptuous, but I was looking for advice on saving weight/components that fit, not about making things sturdier/more comfortable.