Han Solo defeated Fett on accident while Fett was fighting Luke Skywalker. Boba Fett came close to getting slaughtered by Vader but in the end, came out on top.
Look at the price it exacted though, his clone bodies rapidly deteriorated due to those displays of power, I don't think the clone emperor was playing with a full deck; cause he was constantly causing his bodies to deteriorate. The original Palpatine knew that those kind of displays exacted a serious toll on his body.
The game only had half of the story.
Maybe, maybe not, by all accounts Revan shouldn't have been able to beat Malak, but it didn't stop him. While Kreia often lied in KotOR II, I don't think she lied about Revan's power. If you analyze Malak's fighting style, it stands to reason that he used Djem So, or something extremely similar to Djem So. We also have to remember that without his entire memory in that final battle with Malak, he was even more powerful than when he was the Sith Lord.
While I think Revan is often overrated, I think he is powerful enough to be able to take on Darth Vader and not only survive, but actually win. I don't think there is as big of a mismatch in power as people think.
Luke didn't provide much of an assist, it was mostly his trainees, and while they would become the New Jedi Order, they were still only half-trained when they took down Exar Kun.
I'll give you that one.
His original body would have been able to handle it because it is already used to the power inside it. The clone bodies deteriorated because they had no time to adjust to the power within them.
Actually Revan could have beaten Malak easily. Malak was never stronger than Revan. Malak even said so himself. This is a mis-match for one reason. The Rule of Two. Vader is one thousand years ahead of Revan. And since the plan worked, Vader is obviously more powerful than Revan.
Still, the damage Kun could do as a spirit was very good. Not to many Sith can live as a spirit for millenia and then attack the Jedi Order.