It's unnecessary. my assumption is that changing Torch's race serves to make a point about adoption and the definition of family, which fits the FF very well. Changing Doom's gender, IMO, is just changing something to change something and be controversial. I'm fine with change as long as it serves a purpose more than just stirring up chatter. For instance, Bane's new origin story in TDKR was fine since it worked best in the plot. I just can't think of a good reason to change Doom's gender.