I did not interpret the weekly themes as "special" or obscure topics necessarily, past themes have included:
Royalty, Nobility, and the Exercise of Power
and Myths, Legends, and Folklore to name a few, which are not exactly fringe interests.
That said, quite often this sub does treat women's history and gender as special topics comparable to minorities and immigrants but this also seems justifiable to me because as you have said women tend to be marginalised voices in history, despite pretty much consistently making up at least 50% of the population, women are nowhere near equally represented by historical accounts or even in mainstream studies. Not to mention that reddit's own bias makes the need for AH to bring topics like gender, sex and sexuality to the forefront in a non-patronising way because the fact is, most users just do not ask about it as much as warfare, immigration or national identity, and when they do it often comes from a place of misinformation to begin with.
I am also female and I do understand what you mean by saying that it should not be treated as a special interest or a side topic, but I honestly do not feel that is the intent here or the actual result, if anything I think AH does an exemplary job of demonstrating how marginalised voices and perspectives are integral to a complete understanding of history. If anything AH does right it would be that, the only areas that are usually not given their dues are those that are not represented by flairs.