I don't know if you can make competency a required field in any activity or resource. IMO that would lead to undesirable situations where your teachers/instructors will just pick a random competency to be done with it, or don't use any activities altogether.
The way the competency frameworks are meant to be used, is through Learning Plans, that can be linked to cohorts or individual students in your LMS. At a course level, competencies might be useful to be linked to one activity, but not to others...
I think you're right. The more I've been using the system, the more I've come to this same conclusion.
Once competencies are more widely understood, it won't be unusual, I think, that students will ask why we are doing this or that activity if it is not linked to a competency.
Yes this is correct - and the course competencies page lists the activites each competency is linked to - so you can easily scan for competencies that are not linked to anything if that is important to you.