I see cis as something similar to using the phrase neurotypical. It would be hugely offensive to say normal people vs people with autism/Downs syndrome etc. So in that vein I can understand using cis to differentiate between trans women and normal women, and using it makes no difference to me in those discussions
'Women' and 'transwomen' differentiates perfectly well between women and transwomen, who are two different classes of adult humans.
Just as 'horse' and 'seahorse' differentiates perfectly well between two completely different animals. We all know what 'horse' means - we don't have to say 'land horse' to differentiate the two.
Equally, we don't need to make the word 'woman' clearer. We all know that a woman is an adult human female.
However, there is confusion around the word 'transwoman', and other terms such as 'transgender woman', 'transgender female', etc. People are often unsure which way round this is, ie whether a 'transgender woman' is a woman who identifies as a man, or a man who identifies as a woman.
So, if terms need to be made clearer, it is the terms transwoman/transman and their variations which need to change. Using terms such as male-to-trans makes it perfectly clear that the starting point was a male body but doesn't pretend that this male body is now a woman.
And whilst our politicians may be parroting 'transwomen are women', would they be quite so happy to claim that 'male-to-trans' are women?
Words have power. Watch how they are being used.