agreed about the economic efficiency of using the damas but ummm. hmmmm, i dunno but if you look at their defense, even if you have 200% damage dealt to them because of the element, your damage wont be that good because of their high def(i think about 49-52?), i think the "ignore dragon's defense" part of the dragon killer works better at this time
and i think (too lazy to check) the deleters are medium monsters, so daggers only deal 75% dmg and buying elem 1h swords imo is a bit of a bad idea (in the long run no, but atm i got only 19k xD went into bankruptcy after i bought a thief ring
)
and well, rogues aren't really that flexible (imo) when it comes to choosing what monster to grind, so better be a specialist who can kill them asap in order to prevent their lucky attacks to hit you than being a jack of all trades which uhhh... i can't put it into words but i you get the point