Obito can grant parts of his body intangible without the risk of self harm, while Kakashi can do something similar, it's not the same. Kakashi merely used an attack jutsu as a defense jutsu because he had to.
Example: Naruto uses Rasengan targeting Obito/Kakashi's right arm.
Obito: Kamui's arm, making it intangible and counter attacks with same arm once tangibility is restored.
Kakashi: Kamui's arm, losing that arm and bleeding out.
Verdict- Kakashi can only teleport his WHOLE body to Kamui deminsion, others wise he'd mutilate himself.
Kakashi Kamui (Attack)
Obito Kamui (Defense)