Generative artificial intelligence (GenAI) is transforming the L2 writing landscape, particularly in feedback provision. While some studies report positive effects of GenAI feedback on formal aspects of undergraduate writing, few have examined its impact on the academic writing of postgraduates. Addressing this gap, the present study investigates how GenAI- and human-generated feedback affect L2 doctoral students’ English writing. By analyzing scores for two versions of academic paper abstracts (N=71) and comparing the quantity and quality of feedback, the study found: First, both forms of feedback led to overall improvements in writing scores. Second, AI feedback tended to focus on sentence-level issues, whereas human feedback addressed more discourse-level concerns. This distinction was especially evident in the treatment of the second and third of the five major rhetorical moves in abstract writing: identifying the research gap and stating the research aim. Third, AI feedback was typically affirmative, and instilled confidence in revisions, while human feedback often consisted of questions, hints, and suggestions that served as pedagogical guides, fostering critical thinking and learning throughout the writing process. The findings reaffirm the essential roles of both human involvement and modern technologies in enhancing the quality of English language education, underscoring their pedagogical significance.