The English language changes over time. We know that you don’t believe in gender and use woman and man to mean someone’s sex.
We use adjectives to describe subsets of categories all the time. Cis black is obviously a meaningless term but someone might use the term Black African if it was necessary to refer to a specific group of people.
Language does change over time but this isn't an evolving use of language. It's an imposed change in order to provide validation for a small number of people.
'Black African' adds additional information to the term 'Black'. It tells you where someone is from, like 'French woman'. 'Cis' adds nothing because the term 'Woman' already tells you everything you need to know about people who fall into this immutable category. People who don't fall into the category 'Woman' already have words to describe themselves. To follow your logic means Rachel Dolezal can reasonably describe herself as Trans Black.
You are free to label yourself as whatever you like and you can view yourself as a sub set of your own sex if you wish, but words are important. They impart meaning. They are tools to accurately describe our reality. 'Cis' is a nonsense word.
Bringing 'cis women' into common usage is demeaning to those who fought for so long to have women recognised as actual human beings with rights, as a separate sex class with distinct needs, as something more than 'non men'. It's depressing that some women will so quickly give away a word that others worked so long to give meaning to.
