But remember, you weren't flying on DL...you were flying on Song. One goal of Song is to be kept as distant from DL as possible.

Pre-boarding medallions definitely does slow down the boarding process as well, especially on flights that are "medallion heavy," pre-boarding can easily add 5-10 minutes of time.

It's not that medallions can't board fast, its that once aboard they tend to cause backups...sitting in aisle seats which blocks window seats and sitting in the first rows of coach near where people are entering (though with Song this problem isn't quite so bad since the 757 is usually boarded through 2L).