Lol, Kakashi has already stated that it is the same jutsu, and really he could just make the entire rest of his except for his hand, "intangible" (really just using kamui on himself on certain parts of his body). By saying that the nunchaku inside his head prevented him from using his arm, you are saying that he could not make his arm physical if his head is not there, meaning that he must make his entire body intangible, which contradicts what Kakashi said. If naruto could have grabbed his hand then bai and Kakashi didn't even have to be there. Naruto was clearly going to be touched and taken in that instance. He wasn't going to absorb with kamui. He doesn't need his hand to do that. It still doesnt make any sense that he didn't just make the rest of his body intangible and keep his hand tangible, as Kakashi suggests is possible. I blame it on kishimoto's lack of foresight
Are you saying Kakashi could do the same as obito? Cause that is definitely not the case. There is a huge difference between absorbing with your eye, and absorbing with your body. I already answered it somewhere in this thread, why he didn't make his arm 'tangible'.
2nd if it works the same way as you said that would just make it even more stupid for Obito. Since that would mean it requires magnificent control over the jutsu, your body, and chakra manipulation through the eye. So if you took a hit on some body part that wasn't tangible that would put you out of balance, and you could possibly make a mistake, where you closed the dimension on your own body parts, resulting in severe damage.
Anyway as I said, it's not the same, and that is why obito can go intangible, cause he can absorb with any part of his body. And the answer to why he didn't solidify his arm is simple. He couldn't use it to absorb with, but possibly he could use other jutsu, but it wouldn't have made him capture naruto.
Besides it doesn't appear that Obito has a very large amount of jutsus at his disposal, so what exactly would he be able to do? Who says he would even be able to use something like human path in the given situation?
It has clearly been said in the manga that he needs to completely solidify to absorb anything.