He could definately beat her. Kamui is basically a better version of Kaguya's S/T since it has intangibility, and can access the kamui world as well as kaguya's ones.
If kaguya warps them to a world that is bad for obito, he can warp to another one untill she fights him there instead. Kamui can close Kaguya's portals, Kakashi allready did that. That leaves her entire arsenal as Ash bones which Intangibility shits on, and chakra arms which are nothing special.
Killing her is no problem, Objects keep their velocity as the travel between dimensions, so Obito can warp an Ash bone and shoot her with it by opening a portal behind her. No amount of immortality is going to save her from the technique that WILL kill her in the manga.
Long story short, Obito > Kaguya.
You just look at latest chapter than proceed to create a scenerio that you think is check mate already
Kakashi just able to do all that because Kaguya is busy fighting other people's
And what is you true scenerio if Kakashi encounter non distract Kaguya and not relay from this chapter
What about portal grab, what about portal ash bone in closer distance where Objto unable to react
What about gravity dimension that Kaguya can control to make Obito unable to move.
What about hidden inside portal and lunching land changing attack or changing the dimension to acid dimension where Kaguya hiding in the portal
You can't take latest scenerio in the manga and paste it in deferent situation
How about Obito when making intangibility attack and Kaguya open her portal and sent Obito straight to lava sea or acid
Or changing dimension and freeze Obito movement unless he have Amaterasu, he can escape.
What about Kaguya portal duplicate like Obito did to her dimension.
What about Kaguya portal tactical battle
Kamui snipe have it own range that the disadvantages of this technique
If I'm the writer of this fight, I can make 101 situation to take down Obito even by simplest of move
And this fighting thread is nothing in the manga ,that mean I'm free to do anything by Kaguya power. But at one point you'll will saying that I'm creating fanfic because not follow manga fact. And so be it
But I'm know without limit of manga Kaguya can do more
And not Kishi