I get what you're saying. But there are big tells that we can watch for. Theres a big different between putting players in position to succeed who fail vs not putting players in position to succeed. If the opposing offense is constantly a step or two ahead in play calling, and he's always playing catch up. He's failing. Example, blitzing up the middle when the offense dialed in a halfback screen (And before you ask, yes this actually happened in the 1st half when the Raiders put up 66 pts) vs say calling a cover 2 when the opposing offense dials in a halfback screen. 1 is pure failure as a play caller and the other is putting your players in position to make plays. If the players are put into position to make plays, and don't, then you have to look at positional coaching and ask if they're being properly coached up. Or look for talent elsewhere (FA, Draft, Trade etc).
This is what I'm going to be watching for. What I don't understand is why with the Rams was the play calling like checkers where players knew exactly what they should be doing, vs the Chargers the players were constantly confused on their assignment. The simple truth is we'll never know. But its scary to think that he could bring that Chargers defensive philosophy here.