I am going to talk in general terms more so...
A great coach will always adjust his scheme to fit the players he has available... not trying to fit a square peg into a round hole. They take the overall collection of players and tailor their playbook the that roster. Some players may not fit with the rest of the overall group.. but we will leave that to the side in this dis
Certain positions in football a coach can compensate around via scheme and some he cannot.
Hence why the "drop off" in play for certain positions seems very rapid and others seem very gradual in a relative nature.. there will always be an athlete that can distort the norm, but on average.. they will more often than not hold true.
A corner, you can utilize a zone or bump coverage with a rolled over safety to compensate for a lost step.
A receiver routes and sets can be shorted up to utilize their experience in running a quality route to cover for their loss of step.
A lineman hones his craft over the years... maximizing his efficiency and technique to make up for a half second lag in getting set up in pass protection or firing out in a run block... the coaching staff can keep a back, tight end or motion to help offset this as well.
But in the case of a running back.. once they have lost that burst through the hole or that extra gear... their isn't much a coaching staff can do to cover for it.. other than change the percentage of runs vs pass and maybe more rapidly developing plays.. but they can't mask that burst a player has to create yards on his own.. and backs by far have to create the most yards from scrimmage in a season...
Most of the time.. corners fall off fast because coaching staffs are unwilling to adjust to the player and the player is unwilling to admit they can't play the island by themselves any longer.. either they revert to a safety or drop into the slot receivers and less snaps a game.
My opinion from watching and studying the game for better part of three decades and how the game has changed over the years.
"The oranges are dry; the apples are mealy; and the papayas... I don't know what's going on with the papayas!"