Should trust level 4 be able to pin a sitewide banner?

I experimented a bit with hiding some actions from Trust Level 4 back in Dec 2017. Not perfect but it might be good enough as a temporary approach. eg. Choose selectors as per need.

/* personal messages display none wrench leaders */
  body:not(.staff):not(.archetype-regular) .toggle-admin-menu { 
    display: none;
} 
/* personal messages display none individual buttons leaders */ 
/* pin and archive are n/a */
  body:not(.staff):not(.archetype-regular) .topic-admin-multi-select 
, body:not(.staff):not(.archetype-regular) .topic-admin-close 
, body:not(.staff):not(.archetype-regular) .topic-admin-visible {
    display: none; 
}
/* topics display none individual buttons leaders */ 
/* topic-admin-close and topic-admin-visible not in this example set */
  body:not(.staff):not(.archetype-private_message) .topic-admin-multi-select 
, body:not(.staff):not(.archetype-private_message) .topic-admin-pin 
, body:not(.staff):not(.archetype-private_message) .topic-admin-archive {
    display: none; 
}