Your question deserves a very detailed and thoughtful response, but I have to start somewhere. So here is a broad-stroke reply.
Feedback is clearly one of the most important features of motor learning. However, feedback comes in many forms and also in many contexts of application -- some good, some not so good. Most feedback is just junk, and most contexts for applying feedback are not that well thought-out or helpful.
There is first the issue of defining the skill to be taught. This is hardly obvious. Next, there is the issue of the optimal biomechanics and strategy for performing the task (how to move what where). Only after these matters are sorted out can the feedback be designed and used effectively.
In putting, the key task is not that well defined. Some people think that the task is putting the ball into the hole; some think it is putting the ball toward a target with appropriate energy or touch; some think it is rolling the ball wherever the putter is aimed with a stroke appropriate for the distance. Most training aids for the putting stroke simply define the task as making the ball roll wherever the training device is aimed. That's sort of messed up.
Plenty of training aids don't give any feedback at all, but just help the golfer get a good movement done. These sorts of devices are very seductive and misleading.
In motor learning theory, there is a debate over whether the learner needs to learn how to do the skill or whether the learner needs to undertsand how the skill needs to be done and then learn to do the skill. I believe in the latter. People who believe in "muscle memory" learning by mindless rote repetition subscribe to the former.
I believe that the student needs an understanding of how and why the skill is performed in a certain way. This empowers the student to coach himself and to benefit more richly from feedback as practice and performance goes forward in time.
I also believe that most training aids engender dependence on the visual and physical cues (artifically) provided by the device itself, and that these device-provided cues mask and prevent the student from heeding the REAL cues that are actually available during performance.
So I think that training aids have to be evaluated for efficacy and appropriateness in light of expertise sought to be inculcated, and that the device should only be used to enable the student to experience and understand the HOW and WHY of the motor performance in the context of building familiarity with the real cues available during performance. This is a limited use, and not a massive-practice rote repetition with the device. Once the device is used to expose the student to the WHY and HOW of performing the skill in an optimal way, the student needs to get intimately familiar with ONLY those cues that are actually available in real performance contexts. This use of the device gives the student the real cognitive and physical knowledge of expertise with which future trials of the skill can be evaluated in a meaningful way. This makes the real cues and the feedback during actual performance with these real cues more beneficial so that the student learsn specifically from every attempt, faster and better. Overall, this is more of a process orientation to skills development that works well with promoting the student's mastery and "self-efficacy" (I hate this academic jargon).
MANY training aids have implicit in them BAD strategies or movement patterns, or at least encourage students down an undesireable path. MOST training aids fail to show the student much about the HOW or WHY of a movement. Almost ALL training aids are wrongly provided with the advice to use them indiscriminately as often as possible. Practically NO training aids are supplied with good written explanations of the HOW and WHY the device seeks to teach or about the appropriate use of the device.
I agree completely with you that a training device has to be gotten away from, so the student can focus on what he is actually trying to do and how he is supposed to do it correctly.
That's pretty much my broad-stroke take on training devices.
Here's a pretty good discussion of some of these issues: Monica Frank, Behavioral Consultants, St Louis M, Feedback, Self-Efficacy, and the Development of Motor Skills
Putting Theorist and Instructor
Geoff Mangum's PuttingZone
Golf's most advanced and comprehensive putting instruction.
Over 1,240,000 visits and growing strong ...
518 Woodlawn Ave
Greensboro NC 27401