What is the 'System' display option in Views?
Today I was in the same situation, so I decided to look and this is what I found:


  So, for anyone stumbling upon this, 'system' displays are only to override core views (which you do through the System Path Settings area in the Advanced section of views) and I should just be using a page display with a path that begins with '/admin/' if I want to make custom admin views.


Here is the link: https://www.drupal.org/node/2539256#comment-10150524