I think there is a way too much vertical spacing between user defined actions in the list [available under the Actions icon]
It may be that the number of visible actions varies [depending on OS settings / screen model]; but right now I can see 35 predefined actions [and two signs △ ▽ indicating the existence of more content on this list] while at the same time the number of visible loaded files [in the main window] is 38 [when my toolbar and filter are turned off]. And the action list goes from the very top to the very bottom of the screen while the main window has borders and other stuff [that if they were not present, then the main windows would be showing over 40 files]. So it is an obvious waste of space
Ans as the chosen action in the menu list is highlighted, there is no need for extra spacing between them [because the user clearly sees what is being selected]
Most people probably have few actions or have the commonly one used somewhere at the top of the list. But I have around 50 actions and mostly in alphabetical order; and what I could I have already grouped into sub-menus, but for me there is still over 40 often used actions [and by placing them in groups I would sentenced myself for hundreds of additional "empty" clicks per week, just to get to them, instead of just clicking the Actions icon]