A ninja could be horrible at taijustsu and ninjutsu, but incredible with genjutsu.
Like Sakura?? Hmm. We'll have to see more of her.

Another thing. Kakashi doesn't seem to have a bloodline. But he is considered a genius. I think even for Sharingan users who are able to see everything, it would take alot of hard work to copy the technique unless he is a genius who can copy it instantly.