Hagoromo's power was Yin and Yang.
-Asura got the strong Yang Chakra and his father's body.
-Indra got the strong Yin Chakra and his fathers eyes.
Thus Indra could use the Sharingan and Perfect Susanoo while Asura had his Avatar.
And no, Indra wouldn't be a Sasuke or Madara w/ just EMS. His strong chakra came from his father, one of the strongest chakras in existence. Sasuke got that chakra and his Susanoo became the strongest in the manga, Indra has that chakra as well, hence the horns on his Susanoo. So he'd stomp EMS Madara or EMS Sasuke. But since Sasuke got half of Rikudo's Yin Chakra, he's stronger than Sasuke.
Asura isn't a Naruto with more chakra either. He only got some of his father's strong Yang Chakra. Naruto was given all of Hagoromo's Yang Chakra, he has 1 Full Bijuu and 8 pieces of the others inside his body, and he can gather ridiculous amounts of Nature Energy. He's far above Asura at this point. He was stronger than Asura the moment he got his power from Hagoromo.