Kakashi's Kamui is easy to counter. All you have to do is cast a quick genjutsu on him and side step.
Then Kakashi will think you are straight ahead , but you will actually be two steps to the left.
Or make him think you are 2 steps to the right, when you are actually straight ahead.
When Itachi used genjutsu on Deidara, he could still move and run around, while Deidara was still in the same spot.
Madara cast a genjutsu on Raikage A and A was kneeling over while Madara was still hanging around .
Sasuke cast lots of quick short genjutsu on Danzo during a hectic grueling fight.
All you have to do is cast the genjutsu at the right time. Also Kakashi has to go MS to use Kamui while an Uchiha can just use a regular tomoe sharingan to cast a quick genjutsu and evade.