It's not just a dumb rule for no reason. Peaks are significantly sharper and more formal to me. I'm actually not as lenient as on this one. There is no way a notch lapel will ever look as good as peak or shawl lapels on a tuxedo. I guess they are "fine" as in you shouldn't be kicked out of the party for wearing them, but why look just "fine" in black tie, which must be for a big event?