Indra could do anything on his own, I would guess we just don't know what he's accomplished, but he has to of had many things he's accomplished.
Given what little data we have on Indra and Ashura or how much power either of them have, I won't assume Sasuke is stronger.
We just don't know the amount of power Indra could possess. It's possible that even though he couldn't have EMS, that his MS could be me more powerful than a rennigan or rennisharingan, and it's possible that Ashura's avatar could be greater than Naruto's even with kyuubi, but it's hard to know for sure.
Without a good source of information on the battle between Indra and Ashura, their stats, or anything about even what their abilities were, it's hard to say.