Maybe it came out wrong. I am a fan of the character but for the Cartoon description,My guess is because you referred to Cordelia as a "cartoon character" and that "She was only on the show because Greenwalt was a fan and pushed for her."
Tell you what; you bring your Cordelia drum, I'll bring my Kennedy drum, someone else can bring their Connor drum and we can start a band. We'll be the " I hate Cordorennedy drummers" (working title).
On Buffy certainly for the first season she kind of was. Even Joss calls her that on the DVD commentary. She develops in S2 then in S3 they press the reset button after the Xander breakup up until the Prom, where she'd go back to normal developed Cordy. Though until that point she'd show up and say an insult then leave. Ironically Spike, who was brought in as the Cordy replacement, would be a bit similar in S4 "can I borrow a cup of coffee and insult you" . Ie the writers don't know what to do with a character so they just show up an say a witty line then exit stage left.
On Ats she then develops into a great character (until S4 anyway) and I love her on that.
I think (unintentionally) the best thing to happen to the character was Glenn Quinn getting fired as they moved her into his role with Angel.
I'm also glad that we got Your Welcome as it least it let the character go with Dignity rather than just left in a coma ala S4