Obito still wins, but with different attacks such as Gudo Dama explosions, Mokuton, or by outlasting if necessary.
Gai can't even directly hit the Gudo Dama and Flash Bijuu Dama is easily tanked by a defense made of all 9 Gudo Dama together. Naruto's chakra isn't going to do anything serious to Gai. Not only is Gai a Taijutsu user, but the power he's drawing on is far beyond Kurama as a whole let alone a piece of his chakra.
Uh, no. EE failed to damage the Gudo Dama in canon. EE>>>Asa Kujaku. The rest is so stupid I'm not going to waste my time addressing it.