There are horses and there are carts and getting them ordered properly makes all the difference.  
Unfortunately, when it comes to improving center-wide outputs, call centers often have the cart in front of the horse and you don't need to wonder how that works out.
That explains something important about call center results.  If you ask call center leaders to put up their one or two most important customer measures and their one or two most important shareholder measures and you ask them to graph them over time, you will likely observe two outcomes:  1) performance is mediocre (for example 85% compliance with required call components is often considered quite good in many centers), and 2) those mediocre measures are treading water...there is rarely any evidence of continuous improvement in the most critical center metrics. 
Moreover, Call Center performance has been this way for decades.  The problems have existed for so long and management has become so inured that they have just unplugged the smoke alarms.  Why the leaders of the business don't view the situation as a crisis is astonishing.
Though there is rarely evidence of continuous improvement in call center output measures, there is no lack of improvement projects throughout call centers. Every single call center on Earth has projects underway to increase performance.  They could be technology upgrades.  They could be the never ending calibration meetings that will be used to evaluate agents.  They could even be fairly sophisticated Black Belt-lead DMAIC improvement projects.
Nothing wrong with any of these efforts. All might be needed.  All might even deliver value.  But make no mistake, they are all versions of  "the cart."
Dr. W. Edwards Deming, the late godfather of quality and operations improvement, the one who is credited with resurrecting Japanese manufacturing, talked very little about "carts."  Sure, he was a huge advocate of Plan-Do-Study-Act...his version of DMAIC...and a big proponent of control charts to understand variation at the worker and system levels. These were definitely cart-like elements he often discussed.
But the bulk of his recommendations focused on Leadership, their values, and the organizational "system" they created to deliver results.  For Deming, those elements were "the horse."   If you really wanted to deliver value for customers and improve quality, productivity and shareholder returns, Deming was unrelenting in insisting that leadership get the System "horse" in front of the "cart" of improvement projects.
Deming's two big horses were 1) "Constancy of Purpose" and 2) his "System of Profound Knowledge."  Is the call center's purpose clear?  Is it articulated top to bottom?  Is there a constancy of effort towards achieving that purpose?    Is there any evidence it is being achieved?  
Once you have a Constancy of Purpose, whatever it is, he argued his System of Profound Knowledge was the best way to achieve it.  According to Deming, the four elements of Profound Knowledge were: Understanding (Inputs-Process-Outputs) Systems, Understanding Variation, the Psychology of Change, and the Theory of Knowledge.
Deming laid responsibility for quality and performance measures at the feet of management because management designed the System that generates those outputs.  Yes, a call center's outputs are the weighted average of each agent's individual performance, but it is Management that decides whom to hire, how much to pay them, how much to train and coach them, how well the agents' systems work together, the tools and resources the agents have at their disposal, and on and on.
Completely contrary to Deming's exhortations, call center management does just the opposite.  They have the agents under a microscope.  Everything they say and do is monitored.  They are rewarded, but also sometimes threatened under the flawed and destructive mental model that by trying to improve the performance of each agent, the overall performance of the center will improve.  It is true in theory,  but never, ever true in practice and the simple reason is call center turnover.  Call Center turnover is so high it eats the gains of any improvements from monitoring and coaching.  Read that sentence again.
Deming would ask, instead of the agents, why aren't the designers of the system being constantly monitored  to see if their decisions are actually improving call center outputs?
For  call center leadership teams that are ready to look in the mirror, Deming's framework, tailored to call centers, offers the key.  These are the same principles Dr. Deming used to revitalize this nation's moribund manufacturing industry.  The emphasis needs to be on evaluating the system designed by management that produces, good or bad, the outputs of the call center.
Here are a few examples with links back to Deming's framework:
1) Constancy of Purpose:  What is the purpose of the call center?   Is it there to generate Net-Promoters/Word of Mouth in every interaction?  Is it there to just generate industry average returns while reducing YOY costs?  Is it differentiated performance by customer segment that is the focus?  Whatever the purpose is, is there shared vision on that purpose that runs from the CEO/GM of the business and his/her management team (not just the call center leadership team but the business leadership team) right down to the call center agents?  (Constancy of Purpose)
2) Accountable Leadership:  Once the purpose has been established, how are you doing?  Continuously improving?  Does leadership have the willingness to a) define the metrics that indicate progress on that purpose, b) display those metrics on longitudinal charts (preferably control charts), and c) publicly state whether they are getting better, getting worse or treading water? (Constancy of Purpose, Understanding of Variation, Theory of Change)
3) Causality at the System Level.  Since Y = f(X) (i.e., Y is a function of X), once the Big Y output metrics have been defined and plotted, what is the management team's theory of the Xs that drive those Ys?  Is it written down?  Is it testable?  If you are able to drive systematic improvements in X's, do you see any change in the key employee, customer, and shareholder Ys?  If not, does your "theory of the system" need updating? (Understanding Systems, Theory of Knowledge)
4) Agent Management:  Since you think agents are so critical to your success that your are constantly monitoring them, timing their bathroom breaks, and making sure they are exactly where they are supposed to be at every moment, how much effort actually goes into ensuring you are hiring the best agents and making it so the best agents don't want to get off the phones as soon as they can? Is there any effort to look for real statistical differences in agent performance vs. the typical (and destructive) top/bottom 20% view that every single system produces? (Psychology of Change)
5) Process...Designing Quality In:  Have the Required Call Components (RCCs) been defined by call type?  Do the agents know, by call type, exactly what they are supposed to do in their system and say to customers?  Do you just hope the agents do what they are supposed to or have you done any error-proofing to bake quality into the process thus ensuring that at least some of the RCCs are done exactly right on every call? (Understanding Systems, Psychology of Change)
There is obviously more to Deming's framework.  But I hope this gives you a flavor for why Deming was so focused on the System and its design and so much less concerned with the individual workers in that system.
It is this kind of thinking that helped Japanese manufacturing rise from the rubble of WWII into a global juggernaut.  Once the US woke up, these exact same principles also rebuilt American manufacturing after it got its lunch eaten by the Japanese in the 70s and 80s.  
Deming's framework, tailored to call centers, can easily do the same for any leadership team that is tired of seeing their barely mediocre output measures continue to tread water or who are under the gun to drive dramatic change.
Need convincing?  Look no further than the title of Deming's seminal publication on his approach:  Out of the Crisis.