Add readers to a node in one operation vs N

[MrCreosote]

No idea why I did it this way in the first place...
https://docs.mongodb.com/manual/reference/operator/update/addToSet/#-each-modifier

[MrCreosote]

https://docs.mongodb.com/v3.6/reference/operator/update/addToSet/#each-modifier

[MrCreosote]

No idea why I did it this way in the first place...

Probably because adding multiple users to a read ACL at the same time virtually never happens.
IOW, this is super low priority. Adding a single reader to multiple nodes would have a much bigger performance benefit in KBase land.