I come from Logic, which has a “Collapse view option.” This makes it so the piano roll collapses to only view the notes you have in your parts. To me this never made sense in the key editor (though I can imagine rare instances where it could be useful) but it makes perfect sense for a drum editor!
I would be awesome if Cubase could have a similar “Collapse view option,” to show only the notes / midi events that are in the editor. This would be great in the drum editor to only show the drums that actually have notes recorded on them. For example, not using the cowbell, Tamborine, vibraslap, bongos, etc - you no longer see it in the drum editor. Or better yet, say your beat only has bass drum, snare, hat & cymbals - hit this view option to only see these events.
Hopefully this makes sense and might be implemented.