Once again, Katon are only
incoming attacks in the contrary of Chou Mokuton sashiki attack that was spammable,
it would only traverse during a certain moment.
Look carefully at the pic where Juubi, Madara and Obito launched their attack:
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Look at the bottom particularly. We read the manga from right through left. Bottom right panel we see the group unbalanced(due to Juubi's attack), so at that point, the Katons didn't reach.
Bottom right middle panel, the katons still didn't reach but was close to it. The katons finally reached bottom left middle panel where we see the alliance protected by Naruto's cloak.
And bottom left panel we see Madara and Obito prepared to launch other attacks, that we see on the page later:
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On the same page(bottom), notice that the katons just seems to have traverse the alliance. That means the katons didn't last that long on them. The moment it touched the alliance, it travelled very fast to pass through them. That's the process of katon technique
The katon despite impressive in size is only an
incoming attack that travels very fast from one point to another, not a spammable attack like Chou Mokuton sashiki that Hiashi countered during a great while to save the alliance