Long time ago, when trees were big, our small team was migrating old LMS solution from .NET Nuke to Drupal 7. It took tremendous amount of time to map 900+ tables to Drupal entities and custom tables (custom entities were still causing pain in D7).
After the migration, this LMS lived for about 5 years serving its students. Nothing is permanent in the web world and it bacome apparent that D7 is approaching it's EOL. Product owner decided to proceed with migration to Drupal 8. Though, this time we did not start from bare bones Drupal and used Opigno distribution as a foundation for the updated LMS.