Well, I know this much! He has lost to 31 teams, and only made the playoffs once. He lost first round. If he was good. They Raiders wouldn’t have got rid of him
You start as long as he has for bad teams, of course you will eventually run the table in Ls.
Teams move on from players for many different reasons, including having an incompetent HC that figured he could convince one of “his guys” to come in and be the starter.