> extra capabilities you get from an ActiveRecord framework such as full-stack admin pages

The naive "here's a row-level view of the database records" that things like ActiveRecord/ActiveAdmin give you by default are entirely inappropriate for any line of business administrative interaction. Line of business admin sites should be workflow based and focused on surfacing specific information needed for processes outside of the admin site itself. Non-developer staff should not be expected to interpret the state of rows and relationships among the tables.