Exploring the disciplinary interface between English for Specific Purposes (ESP) and World Englishes (WEs)—two fields with overlapping concerns in global English use, pedagogical relevance, and sociolinguistic legitimacy—this study investigates how their theoretical and practical synergies can inform TEFL and ESP research, with teachers’ attitudes serving as the focal point; specifically, it examines Iranian EFL and ESP instructors’ perspectives on integrating WEs into ESP instruction and evaluates the alignment of current ESP curricula with learners’ authentic communicative needs, particularly in spoken performance; employing a sequential explanatory mixed-methods design, the research engaged 64 participants: 32 TEFL, 17 EFL, and 15 ESP teachers (balanced by gender, 16 male and 16 female, aged 30–67), who first completed a validated quantitative questionnaire assessing attitudes toward WEs, syllabus design, instructional methods, cultural representation, and perceived student outcomes, followed by targeted open-ended items for qualitative elaboration; descriptive and inferential analyses revealed overwhelmingly positive dispositions toward WEs across all groups, with strong consensus that ESP instruction should be learner-centered and goal-driven—prioritizing students’ academic or professional objectives over rigid native-speaker norms; notably, more than two-thirds of rESPondents (68.7%) expressed dissatisfaction with the current ESP syllabuses, citing irrelevance, rigidity, and lack of contextualization; however, discontent with teaching methodologies, cultural content, and textbook materials was significantly more pronounced—and statistically distinct—among ESP teachers (χ² = 9.32, p = .002), suggesting heightened awareness of pedagogical misalignment due to their specialized instructional role; critically, all participant groups reported near-universal dissatisfaction (95.3%) with their ESP students’ speaking proficiency, describing learners as hesitant, lexically limited, and unable to engage in discipline-specific oral interactions—dESPite often achieving competence in reading and writing; this disparity points to a systemic overemphasis on receptive and written skills at the expense of oral communication, undermining students’ preparedness for real-world academic or workplace demands where speaking is integral (e.g., conferences, consultations, presentations); consequently, the study infers that prevailing ESP courses in Iran inadequately address learners’ holistic language needs, particularly speaking, and calls for curriculum reform grounded in WEs-informed principles—such as plurilingual competence, functional appropriateness, and local voice—that validate diverse Englishes while equipping learners with pragmatic, context-sensitive communicative agency; such reform would require re-conceptualizing ESP not as a transmission of “standard” English for static purposes, but as dynamic, identity-affirming preparation for participation in global professional communities.