Modern technologies continually advance digital diagnostic assessment tools that provide tailored, immediate feedback to L2 learners’ writing in higher education. However, the synergetic role of L2 teachers’ contextual and professional attributes, such as institutional affiliation and teaching experience, has remained insufficiently explored in pedagogical diagnostic assessment. To explore such nuances, this quasi-experimental study cross-examined how novice and experienced ELT professors employed diagnostic assessment in physical and virtual classrooms at State Universities and Islamic Azad University (IAU) Branches in Iran to improve EFL undergraduates’ academic writing performance. To do so, 320 EFL undergraduates were non-randomly selected and assigned to eight groups, grounded in ELT professors’ teaching experience (novice versus experienced), university affiliation (State versus IAU Branches), and diagnostic assessment modality (in real classroom versus Google Meet). Participants who collaborated on writing tasks received teacher diagnostic assessments and ratings across 14 sessions, based on the IELTS writing task rubric. Incorporated repeated measures two-way ANOVA tests demonstrated that ELT professors’ productive classroom-based diagnostic assessment was not interfaced with their teaching experience or university affiliation. Yet, their e-diagnostic assessment, teaching experience, and university affiliation showed notable interactions. In other words, experienced ELT professors at State Universities and novice ELT professors at IAU Branches achieved better results with e-diagnostic assessment than their counterparts. These controversial findings imply the superiority of ELT professors’ digital literacy to teaching experience or institutional affiliation in virtual L2 learning platforms. Moreover, regular and systematic institutional support for technology-mediated EFL learning is endorsed in higher education.