From my experience, more "unintelligible" are group discussions than presentations as students are less capable to be articulate and coherent in their debates than PPTs. This is, I believe, for the requirement to be unscripted and spontaneous when participating in arguments which is not quite the case when giving PowerPoint. All in all, heavy accents are one thing, nonsense mumbling another. How serious pronunciation problems can be prevented, or perhaps reduced, should be looked at prior to or at the entry to such academic programs.