Kamui doesn't defeat anyone..
People Kamui doesn't defeat anyone.. If you have looked at the times Kamui was used, it was to always avoid something.. Its not overpowering someone, or making yourself strong enough to hit them. Kamui is a simple teleportation technique. That is why it doesn't count as defeating someone.
This is why all the comments about Kamui like, " Kamui solos hashirama/Madara/ Naruto" are a fail.. cause all they do is teleport them to a another dimension. I don't see how thats soloing the person.
Sure Kamui can be used to defeat the enemy.. Obito uses it all the time.. he makes is own body go to the other dimension and etc. BUT when you use it on another person it is a simple teleportation.
If teleporting someone to a different place meant defeating someone then it would count as defeating, but for now it doesn't.
Defeating someone in a fight means, you physically overpower them and prove that your superior.... not teleport them to a place where you can't touch them. lol.
I hope I have made my point.