I covered the Indispensable premise earlier with the defense.
An Indispensable is defined by the distance between the starter and their replacement within the context of the overall value to the offense. So crowning Gary Johnson King of the Defensive Indispensables wasn’t very hard. He’s a very good player who is primary to the defensive scheme and the replacement quality behind him is a marked drop.
Offense is trickier.
The Indispensables isn’t about identifying our best players per se. Even a marginal starter with a huge drop off behind can be pretty indispensable. You also have to look at what the offense asks of its components. Some positional deficits can be schemed away. Others – like QB and OL – stubbornly sit on your white board no matter how you draw up the play. Keep that in mind as I state my case.