One tired analyst, a structured scoring sheet, a queue of similar cases behind. The letter that wins is written for that workflow.
The issuer's analyst is the audience for the rebuttal letter, and the analyst's workflow is short: about 90 seconds per file, a structured scoring sheet open on the screen, a queue of similar cases behind. The merchant's letter is one of perhaps 50 the analyst will read that day, and the disposition is largely decided before the analyst has reached the second paragraph.
Most rebuttal letters lose on line one. The analyst is scanning for the reason code citation that anchors the case (Visa 13.1, Mastercard 4853-NA, or whatever the issuer filed under), the labels that identify the evidence being supplied, and the specific answer to the question the issuer's questionnaire is asking. A letter that opens with a polite paragraph of context fails this scan because the analyst never reaches the substance. A letter that opens with the citation, labels the evidence by what it proves, and answers the issuer's question in the second sentence wins disproportionately, not because it makes a better argument, but because it makes the same argument legible in the time the analyst has.
Writing for that workflow means the reason code citation comes first, every evidence reference is labeled with what it establishes, and the issuer's specific question is answered in the body before any context the merchant wants to add. The reader is one tired analyst with a scoring sheet open and 89 cases left in the queue, and a letter written for that reader wins more often than a letter written for an imaginary audience that has time.