You mean the army that came along
after he was already defeated? Naruto and sasuke already beat him by that point, they needed the army to free the bijuu; since naruto didn't want to kill obito which would result in the bijuu dying.
Minato, tobirama, tsunade and all those others were literally fighting the shinju
only by that point. That had absolutely nothing to do with obito who was constantly running from PS-Kurama. I suggest you go re-read the manga if you honestly believe Omnyoudon can affect madara. Sasuke was casually tanking it with a V3 susano'o and Cursed seal. Madara has V3 + sage mode + healing.
Anyway, Without naruto's BS the guy would be sliced in half. That's a kill shot.
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