How Long Had The Klingons and Vulcans Known that the Klingon Empire Was Doomed?

A departure from the chickens, AI video generation, commentary about news and opinions brings us towards something which I observed while re-watching Star Trek 3: The Search for Spock.

There were lines uttered by Christopher Lloyd's character, Kruge which caused me to wonder:

had the movie creators intended an arc about the decline of the Klingon Empire?

This could've been unintentional on their part, perhaps even deliberate to demonstrate the failures of a militaristic-based economy.

Let me know your thought, opinions and comments.