I would say that it's a shoehorned way for a world to exist, rather than say it's "valid." Azeroth is basically a world with gender equality. Sure, there are more male leaders, but it makes no real difference to what the society views as the role of women and men, which seems to be identical in Azeroth.
The problem isn't a male led development team. They have less to work with for female characters because of the nature of Azeroth - one of total gender parity. Maybe that decision is something that acts as an overall positive for female players (it's not hard to imagine a WoW in which classes also had gender restrictions). But it creates a less believable environment for a female main character writing to flourish, because it's just that much more removed from real world parallels.
The answer is not to write a character without gender in mind. That's just introducing weak writing at the outset. The way I see it, the answer is probably more along the lines of first reaffirming that gender actually has meaning in Azeroth. Without that, all you've really got is a crowd of people wanting to shoehorn in a gender designation on someone who is powerful or a leader without any actual meaning to the gender. In that situation, there's little reason not to just make the character a man, since that's a lot more relatable to actual history and seems less forced.
It also doesn't mean there can't be a reverse situation for a race. Night Elves HAD the reverse situation when they were introduced. And gender roles were also obliterated for them in WoW. I personally think the game would have been better if say, a female night elf could not be a druid, but could be a priest and warrior, and a male night elf could not be a priest or warrior, but could be a druid. That decision's long past, but it wouldn't be a bad idea to maybe reenforce that Night Elf society actually had this gender division for THOUSANDS OF YEARS and show what effect that has on younger night elves today.
I disagree with this. Who are you to say that a world with gender equality is invalid? If you were saying that presenting an existing world like our own as having gender equality, then maybe your argument would have some merit. But saying that it isn't a valid way for a fantasy world to exist is pretty ridiculous, especially given that even the one race it has in common with our real world isn't really the same. Humans in WoW are not earth humams; they have their own backstory, history, and culture. And even if you could convince me that it was not valid for humans not to have gender roles, humans (contrary to the belief of certain developers) are far from the only race in the game.
Regardless, I will say this; you can't have it both ways. It makes no sense whatsoever to present the world as generally having few if any gender barriers but then still putting them there for important characters de facto, which is almost undeniably a problem with the writing--or a problem with the writers, if it was intentional. My guess, which is admittedly little more than that, as to the root of this problem may not be correct, but the problem itself is still quite real, and the world -has- on the whole been portrayed as very gender neutral, potentially with exceptions such as night elves in the past.
But I do not think it is weak writing to write a character without thinking too much about gender, particularly in a world like this. It may be suboptimal writing, but I will take suboptimal writing over poor writing any day. And frankly, it seems a much more attainable goal. Earth history is irrelevant to WoW history, and your argument therefore falls flat. If the history and general world on the ground in WoW was more like earth's, then it could be applicable.
One reason it is not is simply magic. Physical strength loses a lot of its meaning against skilled magi, and even if you might argue that men of most races are still physically stronger, it is not the case that they are more magically inclined. And while maybe a warrior can fight a mage in pvp for metagame reasons, lorewise a warrior with no magical weapons or equipment is nothing more or less than cannon fodder when set against a mage of any real skill, or any other user of magic. So, it is far more weak writing to default to making a character male because you are male and happen to feel more "right" with that in a world that does not support that attitude than it is to write characters acting as though they were gender neutral.