First of all, we should be clear what you mean by the "ghost-ball system." FYI, I have a complete description with an illustration, article links, and video demos here:
Now, many things can go wrong with the ghost-ball system, as is the case with any "system" (e.g.,
contact-point-to-contact-point,
double-the-distance, or any other system based on "ghost ball"). Some people will have trouble visualizing the necessary contact point on the OB. People with this difficulty will probably have trouble with any "system." Some people will have trouble visualizing the center of the ghost ball (although, I have some resources to help with this
here). And some people will not understand how and when to adjust for
cut-induced-throw (CIT). And most people will not be able to
compensate the aim perfectly for squirt, swerve, and throw when using English.
Therefore, the answer to your question is: yes. The "ghost-ball system" (or any system based on "ghost ball") is an approximate system (depending on how you define "approximate system.")
Now, what distinguishes ghost-ball-based systems from limited-reference-line systems like
CTE,
90/90, and
fractional ball, is "geometric validity" over a wide range of shots. The ghost-ball systems do result in an exact line of aim if the contact points and/or ghost-ball center are visualized properly. And the systems work (geometrically anyway) for shots of any distance (CB-to-OB and OB-to-pocket and CB-to-pocket) and any angle (i.e., for any relative positions of the CB, OB, and pocket). This cannot be said for the limited-reference-line systems unless something is "adjusted" (e.g., vary the bridge length or the "effective pivot length" based on the ball distances and/or amount of cut needed).
All systems require "visual intelligence" (i.e., the ability to perceive points, lines, and angles in 3D), but some systems also need judgment and adjustments beyond the visualization requirements (e.g., because they are not "geometrically valid" over a wide range of shots).
Again, I haven't seen a complete description (with a detailed and clear procedure), illustration, and demonstration of your version of CTE, so I don't know if it fits in the category of the others or not. However, I do look forward to seeing what you eventually post on your blog.
Regards,
Dave