If anything, I think arrows should be increased in power and javelins too against armored opponents. There was a reason that full plate mail became full plat mail. No matter how strong your breast plate is, hundreds of arrows hitting randomly will hit an uncovered spot. However, I can fire about 500 arrows into a group of guys with a cuirass, a helmet and a shield with their faces and next exposed and it won't kill barely any. Javelins are barely better.