Surely being light isn’t the point?
To praphrase, “it’s not the size of the dog in the fight, it’s the size of the fight in the dog”. Taking a 4″ travel bike down the same trails at the same speed as a 5″ travel bike is going to put more stress if anything on it, so it needs to be just as strong.
The point of shorter travel is that it rides a little differently, doesn’t wolow about as much, pedals better, pumps better, etc.