Lightning storms do have a huge amount of heat on impact. About, twice the surface of the sun for half a second. But, normal electricity doesn't have heat, just electrical energy that causes heat as a bi-product. And Lightning spires are not designed to conduct electricity, they just draw it away from other targets. If they had rubber on them, the lightning wouldn't be drawn to it. Most Lightning like, say, Thor's Hammer. only has the energy, no heat.