I wasn't gonna add an electric furnace that turned smelting into just another crafting process. The benefit to the arc furnace is that it doesn't consume fuel, so for recipes that use fuel as an ingredient it simplifies the setup. If you have an automatic graphene setup, it can supply a large number of furnaces. The speed boost also makes it so that fewer furnaces need to be set up.
I wanted the arc furnace to be a late game thing that is useful once you set it up, but that takes some effort to get running. I didn't want the arc furnace to simply replace the oven.