The average protocol now carries 3.3 amendments before completion, up 60% from pre-2015 levels. Each amendment triggers a cascade: revised protocol, updated ICF, amended Investigator's Brochure, sometimes a DSUR. Implementing one amendment takes an average of 260 days from identification to final IRB approval. Traditional medical writing outsourcing, built around word processors and email threads, hasn't scaled with this burden. The model still delivers real value for specialized therapeutic area expertise and flexible capacity, but four structural weaknesses now limit its effectiveness: writer availability determines document timing, with 25% of job postings unfilled for over three months; turnaround time between database lock and submission-ready CSR can delay regulatory filings by three to six months; cross-document consistency failures create compliance gaps that regulators flag as submission errors; and amendment cascades require separate engagements for each dependent document, creating natural version drift. AI-native tools change this calculus. Merck's generative AI platform cut CSR first draft production from 180 to 80 human-review hours while reducing errors by 50%, freeing medical writers to focus on interpretive work that requires clinical judgment rather than structured data extraction and terminology checking.