The Angel spin-off featured several characters who first appeared in Buffy the Vampire Slayer, where their potential was often wasted. Both the Buffy and Angel shows had large casts with memorable characters, and the running themes in both series had attractive young women chasing the monsters rather than vice versa. This new take was extremely popular with audiences then, and Angel took these themes to a darker setting, expanding on the Buffyverse while being a very different show. This tone change gave the characters in Angel the chance to shine in a more serious show.

https://screenrant.com/buffy-the-vampire-slayer-cordelia-angel-op-ed/