Iron wasn't superior to bronze (in the fact the article claims it was worse), but it was good enough and widespread. All you needed was a furnace with bellows, charcoal, and an iron source (which were everywhere). Since everyone had access to iron, no one person/group had an edge over the others and this prevented highly centralized polities from being established.
Bronze it wouldn't matter because I can't get the raw materials anywhere, and so I can't create an army to oppose you.
Bronze weapon technology had a moat because it required scarce, imported resources. Even if they learned the techniques, most people couldn't make them.
The resources for iron weaponry were readily available; they just needed to learn the techniques.