Like I said, the ones running Korea were extremists.
The Chinese were also ineffective in their own right, closing contact with the world, failing to realize they were falling behind and eventually getting their best real estate carved out by several foreign powers. At this point in time (of the conflict), the West had not only caught up, they had exceeded China's capabilites and they had no clue.
As for the Choson Dynasty, they did survive 500 years. That was 500 solid years of non progress, tyranny, oppression and stupidity. No, to be fair I suppose they were pretty effective at the very beginning. That's how they would have come to power. Backwardness, intimidation, murder... That's how they clung to power. Bastards.
When it comes to the whole Choson Dynasty, you will find no bigger hater than myself.