I guess the point is that previously, if I had only a moderate amount of lyrics or chords (or just the song structure with bar numbers), I could see them with the song list open. The right side that was "cut off" was blank space anyway, and I could play with font size a little to make sure I saw everything. It allowed me to see the entire setlist yet also have my notes for the song I was playing. Obviously, this doesn't work for songs that have a PDF sheet or that are absolutely filled with lyrics or chords. But I could still hide the song list and everything would slide over. If I do as you say and set my document viewer up to show only its left half, wouldn't it be stuck that way? I could double tap for full screen but I'd lose my other buttons and indicators.
I guess I had just gotten used to the quirks of the way things were and I didn't expect something like this to change in an update.