An Architectural Advantage of The Instruction-Tuned LLM in Containing The Readability-Accuracy Tension in Text Simplification

The increasing health-seeking behavior and digital consumption of biomedical information by the general public necessitate scalable solutions for automatically adapting complex scientific and technical documents into plain language. Automatic text simplification solutions, including advanced large language models (LLMs), however, continue to face challenges in reliably arbitrating the tension between optimizing readability performance and ensuring preservation of discourse fidelity. This report empirically assesses two major classes of general-purpose LLMs, demonstrating how they navigate the readability-accuracy tension compared to a human benchmark. Using a comparative analysis of the instruction-tuned Mistral-Small 3 24B and the reasoning-augmented QWen2.5 32B, we identify an architectural advantage in the instruction-tuned LLM. Mistral exhibits a tempered lexical simplification strategy that enhances readability across a suite of metrics while preserving human-level discourse with a BERTScore of 0.91. QWen also attains enhanced readability performance and a reasonable BERTScore of 0.89, but its operational strategy shows a disconnect in balancing between readability and accuracy. Additionally, a comprehensive correlation analysis of a suite of 21 metrics spanning readability, discourse fidelity, content safety, and underlying distributional measures for mechanistic insights, confirms strong functional redundancies, and informs metric selection and domain adaptation for text simplification.