Hold it!
Melty Blood Nanaya Shiki does not have the eyes of death power so he’s immensly weaker than Tohno Shiki, he’s “just” a skilled killer/assassin with a little extra
Kagetsu Tohya Nanaya lost his head in all the confusion so he couldn’t be so overpowered and even the normal Shiki had simply frogot about his Eyes Of Death Preception until the end. So practicly Len given the time and opportunity could eliminate Shiki quite fast, if she ever wants to.
Clearly Len+Kohaku=Doomsday
Hell, what supernatural creature could face off with the whole Tohno family, and live about it?
(Hmmm… cant wait for Actress Again… at last, vengance on Roa for everyones suffering.)