The female/female aggression is NOT A MYTH! The percentages are much higher than you state. Yes, often females will get along......for the most part. I think tolerate with dominance behaviors towards a submissive is more like it.
Females, especially the bully breeds, often do fight. It may not happen right away. They may seem like the bestest of friends. But typically, a fight does break out. And when two females fight, they fight to the death. This is how it is in the wild pack. There is ONE Alpha Female and ONE Alpha male in a pack. These are the only two who will mate while they keep their status. Often, the alpha female will chase off her female offspring or even kill off her females. Some submissive females that are no threat will be able to remain, but is often bullied by the alpha female. When that sub fem becomes adult and into heat, that will create a disturbance within the pack. The alpha will try to remove that bitch however possible. The males belong to the Alpha and those are the only ones that will breed with her. Those that are chased off, have to search for their own loner dogs to form a pack, or fight another female for the status of Alpha within that pack. Most packs are made up of inner-bred dogs......The mom is the same for first litters to grand litters. Eventually that Alpha will either get old, mature out of heat, or be killed by a very assertive female from her litter.
Now, there are other female breeds that can absolutley live in harmony with other females. These breeds are not structured around the "Wild pack - Alpha female" mentality. Take for instance border collies, this breed was bred to work, and to work in pairs or packs. So, to better their chances of survival, they NEED to have a pack that is accepting of each other. Bully breeds have not been bred or raised to work in pairs or packs. They often "work" alone. They hunt alone. They survive singly. So, the NEED for partnerships are not necessary, if at all, they are a liability to the survival of self.
I would NEVER suggest a female bully household take on another female bully. In fact, there are rescues who will NEVER, no matter what, place a female into another female home, even if the other dog is not a bully breed. There are reasons for this. And I absolutely agree with it. Having had two females, and they were the bestest of friends, after two years and both into adulthood, there was a fight. And it was the submissive bully that attacked my submissive male and alpha fem boxer. Just last month, I had to break a nasty, blood bath of a fight between a 9 yr old mom and her 4 yr old daughter am bulldogs. Mother was fixed, daughter was not. Mother was absolutely the Alpha fem in a household of two fixed males, one a son and the other a mini-doxie. No warning. Both fems were besties. Then all of a sudden, bam! Lock and loaded!
If there were few issues with fem/fem bully households.....the stories wouldn't be told. To have so many stories of heartaches and trauma, crate & rotates, there has to be truth to the fem/fem aggression. These are not stories to cause a rukus in the dog world. There is nothing to be gained. Like banning pitbulls, will gain the eradication of the breed....therefore, the stories of hype are pushed to gain the goal. There is no goal other than education and awareness in fem/fem aggression.
The truth is....when bringing in a female into a female home, there is ALWAYS THE POTENTIAL OF A FIGHT! More so than two males, or male/females. This can never be forgotten, always a thought it could happen, and best in a confident home. There are some who have had two female boxers in their homes. And I love to hear those stories....because I hear the opposite about 75% more often than the good ones. It's just a risk that the owner should be prepared to take and prepared to crate-seperate-rotate for life. I personally do not feel that this is an ideal situation, as neither dog will get 100% of the attention, always keeping one dog out of the family mix. But some do what they can and do ok with the rotating. I just could not do it, with such a small house or sitting there knowing one is not welcome at that moment.