Why would you say: Ooooh, I want this one, but then only want to do backing harmonies? It makes no sense. Plus Sad Angel is the most Fleetwood Mac-y of all the songs per Lindsey.

This is very true for me as well. Sad Angel is the clear keystone of this release, it really does feel like a single release rather than an EP, to me. If it were framed it that way, I might be more okay with my relatively lacklustre response to a lot of the other material.

Because you realize the song sounds better that way. Stevie and Lindsey harmonize well together, but their harmonies don't always make for the best possible production choice in every line of every song, and you can't always immediately tell where they'll end up fitting well. I'm inclined to think she chose Miss Fantasy too.

The melody of Miss Fantasy doesn't lend to having dual harmony throughout the entirety of the song. It wouldn't work at all. Just because you like a song and want to sing on it doesn't mean you want to sing the whole thing. Of course she'd be doing backing harmony - that's what she usually does on Lindsey's songs.

I just find it unlikely that both of the new songs they are playing live would have been chosen by Stevie. Stevie has Without You, and Lindsey would likely have gotten to have his pick as well.... and since they're doing Sad Angel, I'm inclined to believe that was Lindsey's pick.