Hmm, expressing yourself in terms, which 95 % of the base wont understand may not give you good response, but perhaps enable you to deduce, which responses are worth replying to..
Nonetheless, as I interpret the manga, this whole "lightning edge"-ting, is just a metaphor. I don't think Kakashi ever severed a lightning, I understand it, as Kakashi being very fast and skilled with tajutsu, he himself strikes as a lightning, when using Raikiri, which again is over-exaggerated, since he isn't that fast.
It's not like Amaterasu is as hot as the sun either. It is just a metaphor, meaning it is the hottest thing in narutoverse, and it can burn away anything (ie. so can he sun).