One of the features that I find invaluable in Cubase when composing is the Chord Track. I think that would be a great addition to Studio One.
If you are not familiar with the feature, it's a track where you can input the chords of your chord progressions. Also, it actually helps you to come up with chord progressions because you can choose chords manually, but also get suggestions according to chord proximity, the circle of fifths, common chords progressions and so on.
Now, what's really interesting, is that when you are inputting notes, in each bar you can actually see highlighted in different colors if a note belongs to the selected scale, if it's outside the scale or if it belongs to the chord. For instance, if a bar has C Major in the Chord track and C Major as scale, the note C# is colored as "outiside the scale and the chord", D as "in the scale but outside the current chord" and C, E and G as "belonging to the chord".
For those who are less versed in music theory, helpers to write chord progressions and to input notes knowing if they are within the current scale / current chords, are really crucial