I agree - and offer a strong +1 from me !
At the moment the completiondefault setting of "Advanced features" standardly defaults to "Use activity default", but that default is Manual and imposed across the board on all new activities AND resources. This is often ungainly, confusing, and costing teachers' extra work (individually turning it off or trying to use the Course action menu > More > Activity completion > "Default activity completion" and/or "Bulk edit activity completion" for each course).
The restrictive global defaults have actually made us switch the completiondefault value to "Do not indicate activity completion", and (even) the course default Completion tracking (moodlecourse | enablecompletion) to "No", so as to prevent activating completion indiscriminately in courses. We have to instruct the (interested) teachers about this feature and to show them how to tweak it in their courses.
Yes, I believe there is a need for the fine tuning of each activity / resource default completion setting (also) at the Site administration level. Thanks for bringing up this point.