Well, I think there're simply good coaches and bad coaches regardless of position title. You can't be a good offensive coordinator without fully understanding the intricacies of defensive scheme, and visa verse.
Some Viking examples for you B4P...
Tony Dungy - Defensive Guru for the Vikings.
Led the Vikings to the top rated defense in 1993.
Where is he now?
Leading a leaky (at best) defense, but running perhaps one of the best offensive teams ever.
Brian Billick - Offensive Guru for the Vikings.
Led the Vikings to the top rated offense in 1998.
Where is he now?
Leading an inept (at best) offense, but running perhaps one of the best defensive teams ever.
You work with what you have, and good coaches can work both sides of the line, regardless of personnel.
Back to the question...
Coordinators, per se, are important. But, for the most part, the head coach and management ultimately design the direction of the team.
However, those with more football knowledge than us, usually deem a few coordinators worthy of head coching status every year. Some will pan out, and some will "bite it".
Others, such as Dungy and Billick will succeed, but in ways we never anticipated.
Of course this all does nothing towards explaining how Dave Wannstedt managed surviving 11 freakin' years as a head coach.
