Tin was far more scarce than iron. Iron weapons aren't any better than bronze ones, just easier to source and make. This guy makes a case that iron weapons caused the Bronze Age Collapse.
Bronze is harder and more corrosion resistant, but forged iron (and especially iron that has been reforged) has a higher yield strength and is lighter, allowing longer lighter weapons. Compare the profile of bronze age and iron age swords in any museum and you can see that the bronze blades are shorter and wider that the iron weapons, and they would be considerably heavier.
"Quantity has a quality all its own"