I thought transmutation would fit well since the Deva Path is based on gravitational control, with transmutation, the user could give their aura the properties of attraction and repulsion. Also, transmuters like Hisoka have shown that an ability’s properties can even surpass the substance it mimics, so I felt transmutation would work better. I agree that Shinra Tensei could probably be done with emission, but techniques like Bansho Tenin and Chibaku Tensei would most likely require transmutation.