The problem with PF on D'art is that she's not guaranteed to get full burst ready in the 2 turns you have, even with outside help from himes like Raiko.
Other than that though, I agree about the astraea combo as I've played about with that combo quite a bit myself at one point, and it does synergize quite well with d'art's sniper shot (which doesn't have a stellar landing rate) and thor of course.