Recent paradigms in traumatic brain injury have transitioned from focal-lesion models to an emphasis on diffuse axonal injury and white matter disruption as the primary drivers of cognitive morbidity. This selective review frames information processing speed as the functional signature of this connectivity loss. While processing speed is often theorized as a “cognitive bottleneck” that constrains higher-order functions, we identify critical methodological and conceptual pitfalls in the existing literature. Specifically, we argue that current research is frequently confounded by: (1) measurement impurity, where tasks like the SDMT and TMT-B recruit executive and mnemonic variance; (2) circularity, where speed measures are used to predict time-dependent outcomes; and (3) the neglect of speed–accuracy trade-offs, which may mask volitional cautiousness as neurobiological incapacity. To resolve these challenges, we offer evidence-based recommendations for the clinical setting, including the integration of construct-pure chronometric measures and dual-scoring protocols. We conclude that because white matter integrity functions as a rate-limiting substrate, processing speed must be prioritized as a primary target in early neurorehabilitation. By isolating processing speed from focal-driven deficits, clinicians can more accurately map the path from microstructural disruption to functional recovery. Recognizing this infrastructure is essential to understanding the full scope of cognitive consequences.