After spending several hours in the "music editor" (odd choice; I guess only MIDI counts as "music") I've found no obvious omissions in the MIDI editing features. It appears that Studio One can probably do everything I'd ever want it to do.
That said, I have to admit that the process feels clunky and awkward.
Example. You select the Paint tool to insert notes, which works great (I like the way you can adjust velocity at the same time). But you then realize you've dropped the note on C# instead of C, so the natural move is to select the note and move it. Oops, you just
deleted the note. You have to press "1" first, then you can move it. Don't forget to press "3" again to continue entering data.
I could get used to it, though. You can get used to anything with enough repetition. The developers may have come from Cubase, but it's clear they weren't the ones who wrote the MIDI editor there.