Epics and Features are prioritized by the business and product. They can be expected to slide from iteration to iteration.
Any User Story or task should be expected to be completed an a single iteration.
If you keep having open stories stop bringing in a complete story. Just assign tasks.
Features and Epics are pointed.
Business looks at points earned per year or quarter. Look for trend.
IT leadership looks at amount of open stories and tasks that were moved from iteration back to the backlog. Over the span of all iterations.
This will ensure teams are breaking down work into actionable goals.