I think CAPS was unneccessary, since obviously EVERYONE missed it.
It is not a matter of what weapon he uses. It is how effectivly he makes it out of the 'fire'. If his shield expires, it only takes ONE Old God to obliterate him entirely. Since the shield only covers 5.000 blows and there are 7.500 elementals, it is bound to be exterminated relativly quickly. Then it only takes one blast to knock Kain out of his shoes. He returns and it would take simply another blast to do so again.
The weakened C'Thun instantly kills a target in WoW. I would dare say that the WoW C'Thun is at a fair 5% or less from his original prime. Trough hundred of thousands years of War, only ONE Old God has died. That is NOT because the rest of the Warcraft universe is weak- but because they are strong.
One of Five old Gods does not matter if Kain's shield expires.