Thanks for the comments on my arc. My idea was to make a hero group that only used melee attacks, but it is true that any character that can stay away from them (such as ranged characters or those with slow powers) makes them rather easy. I'll have to think about whether I want to give some of them ranged attacks or not.
As for the second mission, my idea was that, after you cleared the area out, it would be implied that Amy went inside the building as you left. I can understand why it would be jarring to receive text without anyone around, though (it'd be like talking to no one, really). I haven't tried this yet, but maybe I could get rid of the boss, keep it as a kill all, and then once the kill all aspect is completed, another requirement will pop up (that being a boss with Amy being captured in the group). I didn't want to just have an NPC following you around for the entire mission, hence why I opted for how I originally made the mission.
Finally, Westin never really was this much of an A-hole, but when I first made this arc I just pulled an NPC from the standard list I found to be one of the more vile characters. So although I did break out of his personality to an extent, I thought using an already-existing NPC (with a history linked to the Haven House) would be more interesting than just making some random character with a similar personality.
The idea of giving all the Valkyries shields is interesting. I wanted them to be diverse with their powers, but perhaps they'd be more unique if that common element was consistent with all of them.
Again, thanks for the feedback.