First, of men procreates. They simply don't bear children in a womb.
Second nature, in and on itself, cannot discriminate since it doesn't have a will nor intent. That's why we can't say that nature is murderous or cruel either despite the fact that brutal deaths, agony and despair commonplace in it.
It's absolutely the very definition of sexism. Here it is, just for you.
sexism
noun
- prejudice, stereotyping, or discrimination, typically against women, on the basis of sex.
Discrimination on the basis of sex is thus sexism, especially when it pertains to things that women can and might want to do (like soldiering for example). Or things which has influence over their personnal lives, their place in society and the perception of others (like sitting at the administrative head of an organised religion they belong too). It would be like saying that women not having the right to vote isn't sexism because they have the privilege of risking their life and health to bear children.
Equality isn't a point scoring exercise. It's about power, respect, authority and liberty. The Baha'i faith doesn't grant the same liberty, power, respect and authority to women than to men as it reserves its position of utmost respect, power and authority exclusively to men.