They aren't exact, but those are the only 3 arcs that tackle a deeply broken society. Fishman island- racism, Skypiea- Dogmatism, Wano- Xenophobia, and Racism. The difference? The people of wano and only wano didn't acknowledge they did something wrong.

The Kurozumi were genocided for 2 generations (notice how 2 generations is more than 20 years) to the point that everyone thought they were extinct until Orochi. That is thousands, at the least, not a "few". Nothing you've said is wrong and everything you've said I agree with, but you are neglecting the cause of all this, the root problem isn't Orochi or Kanjuro or Kaido, the root problem is wano