The scenario I laid out clearly doesn't involve mods or admins. Though mods' or admins' intervention has the same effect. As pointed out by at least one mod here in the comments, it is problematic from their perspective too, because nuking entire threads by deleting one comment or post is a technical limitation, not a moderation issue
Little add-on: The current behavior kind of makes the creator of a post the "owner" of the comment section. If they dislike an ensuing conversation, even if they're not involved in it, they just delete the post - "Fuck you, you're not having that conversation!". I find that problematic from an ethical perspective.
The scenario I laid out clearly doesn't involve mods or admins. Though mods' or admins' intervention has the same effect. As pointed out by at least one mod here in the comments, it is problematic from their perspective too, because nuking entire threads by deleting one comment or post is a technical limitation, not a moderation issue