What Diamond says that really goes against the "heroic" model of invention is that individual inventors are not really all that important. He argues two things. First, he says that by far most famous inventors did not actually invent something completely new. Instead, they tinkered with something old and improved it. Second, he argues that if the famous inventors hadn't come around, someone else would have made the same breakthrough. So he's saying that invention is a process that is done by building in small steps, not by some genius having an inspiration and creating some finished product right on the spot.
Diamond's argument about the "mother of necessity" also takes some of the shine off of individual inventors. He is saying that these are not people who invent something because they see a need. They are not out to help humanity by solving some problem. Instead, they are just playing around with technology, trying to devise something new just for fun, almost. That takes away from their heroic image because it means that their discoveries are way more random and way less heroic.
Diamond argues that invention is a slow process that is made up of many small steps towards success, instead of the idea that one person has a sudden breakthrough. Diamond tells us that famous inventors don’t start from scratch. They take parts of info and ideas of past inventors and shape it in their own ways, sometimes into new and successful outcomes. However, Diamond believes that if specific people hadn’t figured out the things that they did, someone else would’ve come along and invented their idea eventually. Basically, invention is not about one person and their completed work, it is a timeless process of innovation of people through history.