Well thats the point. Kakashi's nerve isnt mutated...
You are aware that mutation can take place in any moment under the some conditions.He had an eye,that as Tobirama explained is affected by feelings (le eye that reflects feelings,in Tobirama's speech).He was under great emotional stress,so that eye that is so vulnerable to emotions,awake another level.It's not that hard.Kakashi's chakra can be affected by emotion's too.Since the eye that can receive such changes is there,the process takes place.Simple.
Via chakra floating in the air. The eye is linked to both, but since obito has the nerve, the blood, the chakra he benefits from the link from eyes not kakashi(at least not yet). Curse Mark
Seriously,chakra flowing in the air?Obito was far away from Kakashi,not to mention that the panels show that the process took place simultaneously.So Obito not only produced enough chakra to affect his eye,but he sent some in the air,and that amount was big enough to change an eye that was far away from him.Not to mention that he did all this in the speed of light cause those two eyes changed the exact same moment.
Oh god,you're so right,things like that happen every day
And sasuke was just punching some rocks and that was his limit. Also his sharingan always drains some chakra, kakashi is never fully charged + constant running from enemy on top of that, well, u got it? right?
Sasuke had only 1 months training.Kakashi said that it took him days to only get his lighting element down.Meaning he had 20-25 days to learn chidori.Kakashi created the jutsu.He has been training to do that for a long time,we only got to see the first time he used it.Can you seriously compare Sasuke's and Kakashi's tolerant level at that point?Kakashi had been using the jutsu for more than a year,he was way more proficient by the age he killed Rin that Sasuke was when he learned the jutsu.And not to mention that Sasuke used more than 2 chidoris(Gaara fight) and he didn't faint of exhaustion right on the spot.
Even in all his fights when he overused his sharingan he never fainted,he was just extremely exhausted to the level that he can't walk.But 1 raikiri and few minutes using sharingan only to see, got him in a situation like that.Yeah,I get it :|