Well in the first place the cue itself does not "play" at all. Yesterday I did a jump shot clinic and one of the first things I did was to lay the cue on the table and tell it to jump balls.
It laid there and didn't do anything by itself.
There is in fact evidence out there. Both Meucci and Predator have defined deflection as one key performance metric. Both of these companies built devices to test deflection and both companies built cues that have "better" results on this metric as shown by their own testing.
So by using just deflection as one single aspect of a cue's performance it's clear that there are ways to make a cue perform better than another in given circumstances.
The second point is a question of what IS the lowest acceptable standard of construction to be considered a cue.
Your general point is that as a class of cues "custom" ones are not better than production ones in terms of performance.
Of course that general and broad statement is 100% accurate.
And in my time on this forum I can hardly recall any one saying that. In fact it's just the opposite in that the majority of the members say that they can play as well with a low cost production cue as they can with a $3000 custom cue. (individual results may vary).
My point is and remains that by nature there are inherent things about how cues are constructed that make them different and which make them PERFORM differently.
Your point was that a pro player won't miss balls because of the cue rather because of unfamiliarity. If we go back to deflection for a moment and assume that Predator and Meucci are right that deflection is a big deal and the reason for misses then it's certainly true that even a pro could miss because of inconsistent deflection in the cue.
All cue makers know that they can and do build cues that "play" like crap as well as can and do build cues that "play" lights out.
No one to date has put the research together to define and measure all characteristics of why cues feel the way they do and what effect that has on the cue to ball interaction. There has however been some work in this area which has led to greater understanding of deflection. The Jacksonville Experiment, Predator's testing, Meucci's testing, Dr. Dave's testing, the collaboration between Dave and Bob Jewett and their testing.
So in fact we know that a fiber ferrule and an ivory ferrule and a wood ferrule all feel differently, we know that a ferrule that is hollowed out and replaced with foam feels differently, we know that a ferrule with lead shot in feels differently.
We know that a cored cue feels differently than a non cored one. We know that a spliced shaft feels differently to a single-piece shaft.
And so on and so on.
The fact is that a $5000 Scruggs is not by default a cue that "plays" better than a $50 Sterling but the likelihood is that it does and the better the player the more in tune they are with
how much better it is.
Now, as to WHY it's better, well no one is going to fund the research needed to tell you that but any good player can tell you what they think about it.
I will give you an example however that illustrates the point you are trying to make though, which is different from the one you started the thread over.
This is a reprint of something John McChesney printed on RSB years ago.
http://jbcases.com/caseblog/2009/02/22/what-is-the-hit-of-a-pool-cue/