Maybe I'm missing the point here but why is fire better than storm here? I'd say storm is the better choice for soloing stuff like this as you can kite the mobs rather than standing still which is required for fire.
Sorry but not impressed, you can solo NCF easier and faster with lightning imo, for bosses you mostly use MF, when kiting with lightning you can keep yourself healed just using WoH when it has no induction(if you kite right), then you can do way more dps.
The cauldron is faster in fire, i tried. Killing the trash is also a lot faster, granted Thadur and Spider is a lot slower. But all I meant to show was that you can kite effectively without traiting fire. And The Forges of Isengard no lightning RK can do faster, I promise you.