Sometimes a heroic dose of Melodyne is what it takes to get a great mix across the line. Is it the mixer’s job to tune vocals? I’m not sure it matters.
It’s easy for an engineer to get caught up in the morals of preserving a performance exactly as it happened on the studio floor. But an engineer (or a producer, for that matter) isn’t typically getting hired to be a historian. We’re being hired to help make a more powerful piece of art.
It’s our job to make the recording enjoyable, and to deliver a certain message and a certain feeling. Not always to make it highly palatable. But if telling the artist’s story means getting the groove tighter than a drum machine, or minimizing distracting unwanted vocal dissonance, then that’s what it takes.
I’ve sometimes been thanked by artists for making them sound “better than we really are”. They seem to like that, so I’m gonna take that as a sign that it’s part of my job.