This has been my contention for decades: The NFL head coach that decided to attach "coordinator'' to a single offensive coach and defensive coach was a genius.
It was a coach that saw a future, when there would be postgame shows in the media on which members of the sporting public would be invited to call-in and air their grievances over shoddy wins and all losses.
This head coaching clairvoyant was able to anticipate that, after a disappointing offensive performance for their favorite team, the callers would say, "We have to fire that offensive coordinator, Jimbo Jones … this week!''
When it was defense that came up short, it would become, "We have to fire that defensive coordinator, Bloop Blooperson … he's terrible!''
And when the requiem was held at the end of a disappointing season, the head coach could place on the chopping block whatever coordinator the public had zeroed in as the most villainous, thus buying himself a couple more years.
It was in more recent times a lightbulb appeared above the cranium of another head coach (after a season of missed kicks and harmful returns by the opposition) and it read:
"Hey, those coordinator titles have worked great in handing off the blame for failed offense or defense. Why not a 'special teams coordinator' to blame when someone drops a punt?''
Thus, a third coordinator became a staple on NFL coaching staffs (and a share of big-time colleges), even though the chances of someone having expertise in both kicking and, say, catching punts is close to zero.