I think there are flaws with the "two-minimum" rule, and I can see why people say that the rule does not promote equality by mandating that at least two players of each gender are on the pitch constantly. In my opinion, it's unfair that players who aren't as good as others get more playing time because of their gender. Consider these three teams, though.
Team A: Plays in a world without the gender rule but consistently plays with males and females on the pitch. Most of the time, Team A plays with 4 males and 2 females.
Team B: Plays in a world with the gender rule and therefore is required to have a minimum of two players of each gender on the pitch. Team B always plays with 4 males and 2 females.
Team C: Plays in a world without the gender rule and plays with zero or one female on the pitch. 75% of the time, Team C plays with 5 males and 1 female and 25% of the time, Team C plays with 6 males.
I believe Team A is the best at promoting gender equality and Team C is the worst. Team B is not perfect (see above), but does a better job at promoting gender equality than Team C--especially to outsiders. I strongly believe that if the "two minimum" rule was scrapped, a majority of teams would play a majority of their time with one or zero female players on the pitch. There would be Team As, but they would be outnumbered with Team Cs. I think it's best for quidditch if every team is a Team B.
Three Reasons Why the Gender Rule Must Stay
Doing away with the gender rule is supposed to take the spotlight off gender, when really it would add attention to the gender of players. Consider this. Teams tend to try to matchup with their opposition, especially on defense. If one team played with 6 males, the other would be tempted to do the same. I'm not saying they would switch, but if a 4:2 team was losing to a 6:0 team, someone on the 4:2 team would be thinking, "would we matchup better with the other team if we also played 6:0?" This is not even mentioning fanbases. Fans would look for the easiest answer to why their teams was not winning. Sometimes, the fans would conclude it was the gender of their players.
Gameplay and rules would change due to bigger, stronger, faster players. Tackling and contact rules the IQA has developed are meant to protect smaller players, who are predominantly women. Smaller female players who couldn't hit and tackle would not play anymore just because they were required to. Seemingly, there would be no one to protect. People would protest for two handed tackling, other advanced forms of contact and padding. By Rulebook 10 or so, these demands would be met. Quidditch would become much rougher and players would play more recklessly. Bad injuries would be more common. Quidditch is not and it should never be football or rugby nor should it be basketball or soccer. I think right now, teams like Texas and UCLA (that play in a world with the gender rule) find the perfect medium that makes quidditch sustainable.