Why do you think Obito wins this? Please explain to us. IMO, I think either Naruto or Nagato would take the victory for reasons previously stated.
Naruto can't even touch Obito due to his Kamui. Going in Kurama Mode is useless as his TBB can be phased through using Kamui, Big attacks like chakra arms can easily be phased through, and if he goes in Full Kurama mode Obito can use his Rinnegan's Outer Path stakes to bind Naruto with the chains and suppress him as those chains block the Bijuu's power.
If he stays in his Human BM form:
-Still can't touch Obito.
-Clone tactics already failed and Obito can phase through their attacks and each clone can be one shotted using the Gunbai.
-Naruto has only shown to be able to make 3 Bijuu Mode Clones all of which can't use the Full Kurama cloak.
-Any Rasengan or variants can be reflected by Gunbai and absorbed via Rinnegan's Preta Path.
Depending on how the battle plays out either Obito or Naruto could win though I'm sure the latter will win.