I haven't read the original source of this decision about naming the female progenitor of offspring, but I don't think it is intended to replace "mother" for all of those female progenitors, but just to be used optionally for those who don't regard themselves as female mothers, and so don't want to be labelled as one. Getting our (large maternity size) knickers in a twist over it is rather over-reacting. It is only the relatively few trans people who find themselves in a maternity ward and addressed as "Mother" who are affected. If they don't want to think of themselves as the child's mother, that is their choice.
It doesn't alter the biological fact that if a child has been nurtured for nine months inside a body that, at that time, was hormonally female enough to support it, the relationship between nurturer and nurtured is inescapably a mother-and-child one, just as the relationship of a foetus or a newborn child with the provider of sperm is a father-and-child one. That is the most basic definition of the words "mother" and "father". The future nurturing and upbringing of the child once it is born may change its relationship with its parents and/or carers, but up to its arrival in the world, it is dependent on the hormones that keep the womb environment suitable for its survival - and female.