IMO, just because someone has connection to the energies of a certain plane it wouldn't mean that inherently determines anything about their character, i'd view it comparable to saying like, 'you have an inherent connection to the energies of transmutation' or illusion, or necromancy, the energy holds a certain shape and it's effects reflect that shape, the entities who inhabit the planes are formed and molded by their respective energies but their decendants are not shaped by it in the same way even if they retain a connection to those forces.
im not sure if positive and negative energy is the same as good and evil energy is the same as radiant and necrotic but i feel like good energy channeled should cause effects in line with the principles of good: healing, protection and restoration, regardless of who and of what alignment the people who channel it is.
i get that devils and demons are typically based on fire but i kinda wish tiefling's default damage was necrotic to more directly tie their ancestry to the lower planes.