It's not useless, you can still get Broken Hero Swords and Broken Bat Wings. And dat sick Eye Spring yo
I'm referring to the post-mech SE Red Devil, in which Darq mentioned it's drops. They're alright, I guess.
You can't actually obtain Broken Hero swords before Plantera has been defeated, because Mothron will not spawn.
I am pretty sure they removed the chances to get them from other mobs in 1.3 Only the Mothron drops it now
http://terraria.gamepedia.com/Frankenstein http://terraria.gamepedia.com/Swamp_Thing http://terraria.gamepedia.com/Mothron