One can only achieve that balance by admitting both male and female energy. If you say so. If you say so, then by all means form that kind of coven. If you believe magic or worship will only work in one certain way, then for you these will only work in that one certain way. There's a certain constricting dogmatism which comes if we assume these things which work for ourselves must therefore work for others.
Separatism works as well, utilizing other concepts of energy balance and synergy formation.
The basic idea, simplified, is that opposites can be in harmony with each other. Those who hold that this is maintained by a balancing of male and female forces tend to see the world in dualistic fashion. It is worth noting that in most of the Oriental philosophies the idea is to overcome these and other distinctions, finding a more holistic ground, going beyond polarity. In my observation of 13 plus years in the Craft, the only real energy oppositions are NOT in the gender of the participants, but in the patterns each individual has in dealing with energy. THAT's opposition, and that type of opposition certainly doesn' t balance.