This is a well written, sung & constructed piece.
I use correction software to fix harmonies but I usually sing the part as best I can a few times then compile a best of track before doing so.
My parts are messy but the smaller distance a note is moved the better the result and, as mentioned, the variation in timing etc adds more character.
I'm yet to venture from chord tones - that's something I need to learn more about.

Cheers
rayc
"What's so funny about peace, love & understanding?" - N.Lowe