At present, the "Edit" option for each Discussions Topic does not display vitally needed permissions control. In particular, it's critical that instructors have the ability to selectively toggle the ability of students to "Edit and delete their own posts" on a PER TOPIC basis, vs. the current situation, in which a blanket "Edit and delete their own posts" permission can either be allowed or denied, but involving ALL TOPICS for the course!
I find the current situation makes this vitally important control worthless, because whenever I want to toggle permission to for students to edit or delete their own posts, it is specific to a single Topic. An example would be that, when students make posts introducing themselves, I want them to have the option to edit their own post. An obvious and common example of where instructors do NOT want to grant such permissions is when the discussion is graded and students are required to post to the Topic before they can see the posts of other students.
In sum, please move the Edit and Delete posts permissions settings to associate with individual Topics, not the whole Discussions configuration for the course. It would also be nice to separate the "edit" and "delete" permissions (and add an "only if others have not replied" sub-switch for the latter) but I am NOT making that part of this FI since I understand the rule is not to bundle FIs and similar FIs for that already exist.