Completion is a measure of attendance. It tells you a person was present in a system for a period of time and clicked through to the end.
Designing for capability means the experience has to produce something observable: a decision made under realistic conditions, an artifact produced to a standard, a behavior demonstrated with feedback attached.
That has consequences for structure. Time shifts away from delivery and toward rehearsal. Assessment shifts from recall toward application. And at scale, the largest design investment moves from participant materials to facilitator materials, because facilitator variance — not content quality — determines whether the practice actually happens.
The trade is real: capability-oriented design costs more time per participant. The question worth putting to a stakeholder is whether they would rather have completion data for everyone or capability in the population that matters.