Revan was known as being one of the most powerful Sith ever. What did he/she do? He killed numerous Dark Jedi, (The assassins which attack on every planet during KOTOR) He/She killed or converted numerous Jedi, and he/she killed a Sith Lord and his apprentice. Malak and Bandon were no pushovers when Revan defeated them. Bandon would probably kill most of Luke's more powerful opponents. And then there's Malak. He would own any of Luke's enemies. What did Revan do? He/She killed both of them.
Now let's look at the Exile. The Exile killed numerous Dark Jedi, he/she killed three Sith Lords, and he/she was able to cut themself off from the force, which no one else had been able to do.
Here's how the battle would go:
Revan would notice that Anakin was incredibly prone to spazzing, and would taught him until Anakin made a bad move. Revan would then kill him and help the Exile with Luke. Luke, even being very great with the force, wouldn't be able to withstand Revan's mastery of the force. After about 5 minutes, Luke goes down and he might take down the Exile with him. But thats that, and Luke's down for the count.