Definitely missing the theme of the Gunsmith Cats OVA by Peter Erskine!

This list looks like:

1: The song most people probably recognized even if they didn’t watch Evangeline

2-16: Either a recent anime song, or a “classic” anime song regardless of merit of the actual music (ie, we would literally be killed if we didn’t include this, even if the song isn’t musically that good)

17-20: Ghibli