Well the hard thing to determine here is just how good and how often he can truly use it.
I believe that in the time before Kurama powered him up, he could use it about 3/4 times (Once/twice on his Kunai/Once on Obito's shoulder). However, after that it seemed as if he was done being able to use Kamui (as Kurama threw him some chakra when he took over Naruto (allowing Obito to absorb Kakashi).
After that, he had chakra from Kurama and was able to absorb the Hachibi as well as potentially take the Juubi's head.
In addition, Kamui isn't a technique he can just throw out in combat as it takes time to focus it on an enemy. Many of the times he's used it in the war has been on people who aren't moving or trying to dodge his Kamui. Unlike this, it took him time to use it on Deidara who, while note even dodging, was a moving target. Even then he only managed to knock off Deidara's arm!
So people in motion will take more strain/time for him to use Kamui on! Still, there still exists some truth that he has greatly improved his use of Kamui (though part of this may have come from him being within a close proximety of Obito).
So while I don't think Kakashi is a "Solo King", he deffinatly is a tough/aggrivating opponent with Kamui.