I think the only way you can make sense of the whole saga and all the flaws of the prequels is if you conclude Yoda and Obi-Wan underwent a major change in philosophy as a result of the events of the prequels. In the prequels the Jedi are basically super soldiers fighting wars where both sides of the conflict are in service of evil, and Yoda fights multiple Sith pitting strength against strength, employing forces that will ultimately destroy them all. In the original trilogy, Yoda says wars don't make one great, a Jedi should never use the force to attack, and that the evil you encounter is only what you take with you. The Yoda in the prequels is a warrior who fights evil directly and uses clone armies to destroy his enemies. The Yoda in the original trilogy is a sadder wiser creature who learned that pitting violence against violence is not the answer, and chooses to live in isolation rather than fight.
Luke defeats the Emperor by throwing away his weapon, preferring to die and leave himself defenseless rather than give in to hate. He doesn't save his father by becoming more powerful, his supreme act of defiance is rejecting the cycle of violence in pursuit of power. He mirrors Obi-Wan's final moments: in an act of love, he refuses to harm the man he should have every reason to hate. Vader isn't saved by a stronger power, but by mercy. The scenes in Return of the Jedi are so compelling because it's not a battle for who's stronger, but a battle for the souls of Luke and Anakin. Luke wins because he's able to love the monster the Emperor built for him to hate.
The prequels are a loud bombastic mess where the Jedi and Sith are two sides of the same coin, employing similar powers and tactics, a Sith is just a Jedi who favors a different leader. The original trilogy shows the Jedi as rejecting the tactics and worldview of the Sith. And saving someone from the evil within their heart is far more compelling of a resolution than fighting to kill them.
May the force be with us all.