No. I am a woman.
"I'm not a Galaxy! How dare you! I'm a chocolate bar!"
Both trans women and cis women come under the umbrella term of "women", but in some discussions, such as this one, it is easier to separate them and a word you can just put in front of it such as "trans" or "cis" is a lot easier than having to do some kind of waffling phrase like "a person with a vagina" or "a non-biological woman".
the issue is that many women don't have a gender identity and don't identify with the stereotypes associated with femininity. That's the issue with cis, plus the use of it to dismiss, diminish and other women.
Why would not fitting into feminine stereotypes mean that you're not a woman?
If you don't have a gender identity, then you wouldn't be cis, would you? Don't get me wrong, I do know that many agender etc. people don't mind being referred to as women, but depending on the discussion surely they wouldn't be called cis? Or if they were, they wouldn't mind, just as they don't mind being called "women"?
Also, how is being called "cis" dismissive/diminishing?