I think we may be talking past each other a bit. To me cultural relativism is the claim that we have NO grounds for saying one set of values is superior to another. Women's suffrage is the very opposite, It's a set of values people felt passionately about and fought for. And now it's embedded in western culture. And we have good reason to believe that cultures that embrace it produces more flourishing and 'happier' people.
To be frank, women's sufferage really was formulized in 1848 arguably, and then took until 1920 to actually happen. During that time, there was similar discussion to what we're having now. The idea of basic values have changed because of cultural discussion, over the course of decades.
I would argue that equality of sexualities has increasingly become another core value, with the debate of such happening over similar amounts of time. The discussion of course is still ongoing in this field and I'm eager to see what will happen in the future.