Would agree. That's one of my major pet peeves - that the slayers are treated as a bunch of red shirts or cannon fodder. They are barely developed outside of Satsu, Renee and Kennedy - who were all without exception shagging an established character.
I've read fanfic that did a better job with these slayers.

I don't understand what Whedon was thinking. He has 40 issues. Plenty of time to do individual stories about the other slayers. Instead we wander aimlessly around delving into what exactly? Buffy's romantic issues? Didn't we already explore those to death in depth in the tv series?

Now, we have the world shredded and ordinary people killed right and left. I honestly don't see how the writer can possibly bring Angel or Buffy for that matter back from that. It's a bizarre plotline.