I certainly can't fault Fangio's system; it is a popular, much-copied system in the NFL, but great coaches are flexible. They create a system that uses the personnel that they have at the time.
Fangio just flatly refused to do this. Whether stubbornness or just arrogance caused his failure in Miami really doesn't matter; he failed.
He misused his DBs, he misused Ogbah all season long. He misused Van Ginkle early. He was slow to make in-game changes, and worst of all... he lost his player's respect.
He failed... and Grier gave him the quick hook. I wish Shula would have done that with Olivadatti.