Worth noting that historically iron supplemented bronze because it was cheap with raw materials more available. Tin is rare and this is alluded to be the case in Tyranny too with Tiers having no tin deposits. Neither wrought (relatively soft, mallable, tough, produced by smelting ore and forging) or cast (hard, brittle, cast into molds as with bronze) iron are exactly superior weapons grade materials to bronze. That would be steel.
You are right, of course, though we can suspect that Forge-Bound iron actually is steel, maybe even a high-quality one