Coaching has minimal impact. I won the title in the NFFL league and my Head Coach retired.....I hired the best available coach to replace him but he had a different playbook.....My team struggled all through preseason to score.....I finally decided to find another Head Coach with the same playback but at that point only sub 60 Head coaches were available so I hired one....I went on to finish 15-1 but did lose in the Conference Championship game.....After that when I lost a coach in any league I just hired the youngest unemployed coach available who usually rated in the 60s....I've continued to win in all my leagues.....coaching is a novelty and simply not important....the money earmarked for coaching is separate from the player salary cap so its all pointless.

A HC is most important for their playbook. Also coaches impact the progress of players. It was broken down to like 15/10/5 percent from HC/Coord/Position to how much progress your players make in reaching potential. That said, if you have a good roster and GP you can still have success regardless of coaches as mentioned by CJ.

how do you know what plays are in the HC playbook

By his offensive and defensive style and using trail and error to figure out which has what.

JDB has said the playbooks only vary about 10 percent between coaching styles.

Yes. But those 10%... I've never had a HC with Hard Slants.

Preach.
Just preach.
Obtuse is so perfect when used perfectly.
R'amen, brother.