I have no opinion on whether the Sharingan had made Kakashi less proficient as a Ninja, or not. There is really no way to guage that unless Kishimoto explicitly states something to the effect.

What I'd like to see is for Kishi to give Kakashi a Power-Up. Maybe some kind of Chakra storing device. There are at least two examples I can think of of such. 1) Tsunade's Jewel, 2) Samehada.