I haven't tried Krom yet, but I love my two friends Skoll and Hati!

That must have been a bad hit with the mistwalker, or there's some damage modifier that I'm not thinking of. I regularly get over 600 damage from the black metal sword, so I'm sure the damage from mistwalker should be more than what you show. I would expect around 700 damage from the mistwalker.

Of course, Krom should do more damage, but not that much more damage.