This study uniquely combines a Problem-Based Learning (PBL) approach with AI-supported learning strategies to examine the potential effects in business writing. The instructional design was informed by constructivist and scaffolding principles, using multimodal materials to support tone, style, and problem-solving. One action research project examines whether combining PBL with AI feedback tools can support critical thinking and strengthen EFL graduate students’ business-letter writing. Therefore, two classroom cycles were implemented: a complaint letter and a travel expense reimbursement task. Five students completed pre- and post-writing tasks and shared their learning experiences through surveys, interviews, and perception reports. Writing changes were tracked using Grammarly (accuracy/readability), ProWritingAid (clarity/style), and Voyant Tools (lexical density). In Phase One, creativity-related indicators showed larger but uneven shifts (e.g., style +122.2%; vocabulary density +12.4%), suggesting that open-ended problem-solving benefited some learners’ expressive development more than others. Phase Two prioritized clarity and produced smaller, steadier gains in writing quality (0.0–3.1%), along with clearer organization and a more professional tone. Students reported that peer and teacher feedback improved planning and revision, whereas heavy reliance on AI sometimes led to reduced attention to overall structure. Overall, these can support creative expression and analytical clarity through iterative, community-based feedback.