Didn't the sharigan help kakashi and sasuke perfect the chidori.... Yes
But it never powered it up, just allowed them to see an incoming counter attack... As every time either Kakashi or Sasuke used Chidori without the sharingan activated, they have either gotten countered, such as the VOTE 2 fight with Sasuke when he got uppercutted by Nardo. Anyways I'm straying from my point, the sharingan only allows them to see incoming counter attacks, canonically, it has never empowered the moves themselves, like Kyubi chakra does for Naruto and his move