Titanforged? Lei'shen is a fleshy TitanForged and by extent so is Arthas. It would give neither of them any advantage, the fact that Arthas is not only a necromancer but the Lich King with 1000's of souls gives him the clear edge.
You didn't, you mentioned the Lich King overcoming them, but ignore Lei'shen didn't have to overcome Aman'thul, in whatever way you mean it.And where have I said anything about Aman'thul resisting Lei Shen?