https://screenrant.com/cobra-kai-season-4-miyagi-bad-teacher-lesson-right/

By having its characters fail both in karate and in their personal lives, Cobra Kai season 4 proves that Mr. Miyagi’s "bad teachers” lesson was right.

Mr. Miyagi definitely had wisdom that Daniel is still struggling to grasp at the same age that Mr. Miyagi was when Daniel met him.