Beyond Selidor

You are absolutely right — it's a toxic mix of jealousy, self-loathing and a kind of frustration on Faith's part that her best is never going to be good enough, because everyone will always compare her to Buffy.

And that's a very interesting point about Cordelia. I think if the Xander-Cordelia relationship hadn't ended the way it did, Cordelia would've eventually ditched her other friends completely and become a fully-fledged member of the Scoobies. She was on a trajectory of increased self-confidence and desire for truer friends, but the problem is that she entered the group (as something other than an occasional victim to be rescued or source of transport) as Xander's girlfriend, and nobody was going to take her side in the breakup, even though she was in the right.

I wish we could've had some more Faith/Cordelia scenes in Angel once they'd both grown up a bit, to be honest.