He means that the dmg damage reductions from iron set will be doubled cause you are using 2 different weapons.i dont think so. the ppl i vs have iron sets about 95% of the time and i still spam 600-700(lowest is about 500-550) so ur saying i would spam 1k+ on my screen if they didnt have iron set? i think not :P
EDIT: i have dual wield btw xD[/b]
Let's say youd hit 800 with rappy (Im not counting those 300 dmg regardless of def), so iron set reduces it to 0.9 * 0.9 * 800 =648
But with duals (for example spear + club) if youd hit 800 and enemy would have 20 club and 20 spear def means hes "double" the amount of weap def.
Im not sure about this calculation but 0.9 * 0.9 * 0,9 * 0,9 * 800 = 524