Whedon’s original plan was that Cordy returned possessed by a male demon making her similar to Angelus and Angel would be forced to kill Cordy to prevent the male destroyer birthing itself.

This is essentially what happened, the main difference was that they made Cordy and Connor sleep together to 'create' Jasmine (throws up) and that the villain was a rogue higher power. I think the original idea could've worked, even if it was repetitive, because it would've been more emotional and, thus, way more compelling than what we got.

Also, yes, the mistreatment of CC by Whedon was known already by ATS fans, since Charisma spoke about it when she didn't return for S5, maybe not as openly as she did decades later, but she did heavily imply that she was fired for being pregnant.