For the record the
defaults write com.cogsciapps.hook background.app.mode 1
command will also remove it from Force Quit menu and App Switcher.
We considered making it the default (and did so in a public beta) of Hook but we then decided against it.
Users can keep Hook in the Dock without putting it in foreground mode if they want. Just drag and drop it there. I think that’s good for onboarding but after that not as much.