This review provides a comprehensive synthesis of the current knowledge on polyamide (PA)-based materials by integrating data from peer-reviewed literature, technical standards, and published experimental studies into a unified analytical framework. Moving beyond generic material comparisons, this study investigates the fundamental molecular structures and structure–property relationships that dictate PA behavior under demanding operational conditions. The manuscript identifies the specific design constraints, thermal stability, creep resistance, and long-term durability factors that limit or enable the realistic substitution of metallic components with polyamides in high-performance sectors such as aerospace and robotics. Furthermore, we critically analyze the integration of PA in additive manufacturing as a driver for the circular economy, weighing the energy efficiency of polymer recycling against complex environmental drawbacks, including microplastic generation and fossil-fuel reliance. Ultimately, this review establishes a scientifically rigorous selection framework based on performance criteria rather than superficial property descriptions.