<h4>Design for Manufacturing and Assembly (DfMA) has evolved into a broader Design for Excellence (DfX) framework, which considers factors like quality, time, cost, functionality, safety, and sustainability. Generative Artificial Intelligence (GenAI) enhances DfX by quickly generating a myriad of design options, evaluating their performance, and optimizing them based on some predefined excellence criteria. However, this advancement has raised concerns about GenAI’s potential role in competing with or even replacing human designers. This paper argues that human and AI designers are not competitors but complementary partners in achieving DfX. Through mathematical modeling and a case study, this research shows that while the increasing computational power allows AI to enhance the generation, evaluation, and optimization (GEO) processes, they remain computationally demanding. Human designers' intuition and heuristics can efficiently eliminate unfeasible 'solution spaces' and guide AI toward plausible solutions, avoiding the high computational costs. AI excels at quantitative tasks, while human designers are adept at addressing qualitative, intangible aspects such as aesthetics, ethics, and well-being. This study provides an evidence-based perspective to comprise the polarized debates about the role of human designers in the age of GenAI.</h4><p></p>