Kata is the lesson plan, not the lesson. If students never practiced a single kata, karate would survive intact. I am certain of this, provided that instructors hew close to the lessons outlined in the kata. That’s right, lessons outlined, not described in full, in the kata.
In a recent [discussion] on the subject of bunkai I submitted a clip of a shoulder throw to illustrate an application from pinan sono go. [A skilled instructor] pointed out correctly that kata can’t teach students how to throw. I would argue that that it is the teachers job. That karateka are unskilled in shoulder throws is not the fault of pinan sono go. It lies to the instructor to develop that proficiency in his students, or not. An instructor might not see shoulder throws in pinan sono go. The Roshomon effect. That is fine too. The instructor is free to teach his or her own interpretation.
I believe it is a mistake to let students perform kata over and over again, like folding 1000 paper cranes, in the hope that something magic will transpire. It is not that repetition is bad, only the hope that something magic will come of it. Note, I am not criticizing the tried and true method of getting to Carnegie Hall (practice, practice, practice.) Just observing that practicing pinan sono go 1000 times, will get you no closer to executing a shoulder throw than doing the kata once. Again it falls to the teacher. Kata is the lesson plan, not the lesson.