It's as fair or unfair as any other example of natural variation. Different than changing the definition of a protected category in a way that negates the reasons for the protection. If you want to change that definition without destroying it you have to find compromises that won't include everyone.

ok, this is good, you want to talk about definition what is your definition of woman that excludes all trans women and doesn't exclude any cis women?

trans woman is also a protected category, unless the transphobes get their way