I'm not sure there's a definitive answer to this question, that fits everyone's needs, anyway ... let alone a simple one.
Bottom line? It's a strange & unpredictable, synergistic combination of operator knowledge, skills, mental & emotional state, ability to function well under REAL stress, equipment functionality & ergonomics, and probably some indefinable attributes (can anybody say "luck"?) ... that create the best chance for "success" in the real world.
You know the place I mean ... where the rubber meets the road.
There ARE some thoughts I've had over the years, though, whenever someone comes back from some High-Speed/Low-Drag school and tries to reinvent the wheel yet again ...
First, just because some instructor likes it, and can do it well, doesn't mean it intrinsically has merit.
Some very attentive & eager students can simply fail to recognize and grasp important details that can result in something completely differrent being brought back home. Sometimes this is intentional, with the best of intentions to "improve" upon something neat & new, and sometimes it's simply the way different people see things differently. Think "rumor control" and how information is ALWAYS accurately repeated ... NOT.
Some instructors are "technicians", even if once upon a time they "went there & did that" ... and are as capable of later learning bad skills and habits as anyone else.
Just because familiarity can breed contempt, complacency and lessened respect for something ... especially a skills "technique" ... doesn't mean it's necessarily the case.
"New" can sell, while "old" and "available anywhere" doesn't necessarily draw either students, or money ... Insert words such as "TACTICAL", "Advanced", "COMBAT", etc., etc. and it can be resold all over again.
Teaching to the "lowest common denominator" of student is often successful ... and that's exactly the level of information everyone brings home ...
Different people, different "jobs" (L/E vs. Civilian students), different learning goals and objectives, different weapons, different physical abilities of folks ... can all result in different applications of some technical skills, and affect how these things may be taught.
On the other hand ... Half a dozen students may give half a dozen different reviews of what was taught, even if the subject matter was presented to all of them at the same time. Who got it "right"? And what's "right"?
We've had the technological ability to develop tools that throw lead rocks, powered by a deflagration of some powered propellant, for more than a couple of hundred years now ... While the technology has improved rather dramatically, the reason for the "need", and the physical abilities potential of the "users", haven't really changed all that much ...
New techniques require PROPER repetition in order to be accepted into the training skills "databank" ... think muscle memory, and the body's ability to develop "new" neurological pathways after a reasonable amount of intentional physical repetition.
On the other hand, diligently practicing something incorrectly ... such as an improperly performed technique ... can also, unfortunately, result in success ... at "perfecting" the improperly performed technique. One step forward and 3 steps back ... I've worked with a few folks that practiced their less desirable habits or techniques, and got better at doing them wrong.
What price success?
I could go on & on ... but my wordiness is boring ... even to me
... and everybody else here can offer endless versions of similar thoughts.
A couple of last thoughts, though ...
I've also seen some folks return from an outside school and become firmly against using the slide stop to release the slide after reloading. Ditto while training new "lateral" cops from another agency, and one where they were using a weapon which lacked a slide-mounted decocking lever ...
After the first several instances of them releasing the slide using an overhand slide grasp ... and engage the slide-mounted safety, resulting in some unanticipated peace & quiet on the firing line ... we revisit their physical technique in light of how their previous training MIGHT conflict with their current issued safety equipment. Of course, we've also seen instances where the technique was simply performed WRONG in the first place, and it resulted in the shooter sweeping their support hand with their muzzle after the weapon was reloaded and ready to fire.
There are several ways to get to the same destination, and sometimes not every technique may prove to be best-suited to every shooter and circumstance. Good instructors can recognize instances where some lattitude can be allowed in order to best suit the training to the individual student. Sometimes, as "students", even instructors ... or other knowledgeable and well trained shooters ... we may be too intimately involved with the problem to see the best solution. Having an "external" instructor's viewpoint is sometimes not only beneficial, but necessary, in order to properly diagnose and evaluate the performance of a technique ... assuming the technique is "worth" performing.
Sorry, couldn't resist.