I realize that there's been a lot of work behind the drop-buttons, but the fact remains that a) they make assumptions as to which is the most frequently used operation and b) they hide the rest of the operations an extra click away from the user.
Can we have it so that when there's enough space, the operations are displayed as a horizontal list of links (or buttons)? The menu link edit page makes a good use case...
Drop-buttons work great for small screens:

In wide screens (Backdrop/D8) we "force" users to make an additional click while there's so much wasted space:

Let's make operations work like D7 in wide screens in order to spare the users the extra clicks:

Recent comments
I don't think there is currently a way to set back references in bulk for existing books that already reference an author... I believe you can do this with CER through the UI...
Backlinks for Entity Reference?
If choosing the Views approach you can also use https://backdropcms.org/project/eva which allows you to place the list with more flexibility.
Backlinks for Entity Reference?
Thanks. It still took a lot of trial and error for all the settings within the settings, but I eventually got it to display based on these instructions.
Backlinks for Entity Reference?