> if your audience doesn't have a common frame of reference for your words, there's a not-insignificant chance that the metaphor will either fail to convey meaning or, more likely, will convey a meaning wholly at odds with the author's original intent.

If I rephrase this as "your audience needs background knowledge to understand", then this is actually identical to knowledge. Especially when it comes to specialised knowledge, such knowledge can only truly be gained if the required background knowledge is present.

The informative statement "traffic consists of automobiles" will not be understood by anyone without the background knowledge of what an automobile is. Entire scientific journals exist which would be completely incomprehensible to anyone except experts in that scientific field.

In other words, I don't think you've found a flaw in the use of metaphor, so much as you've found a fundamental challenge to effectively communicating understanding in any way at all.