To be clear, I think that the best person should get the job but that it’s more likely that you will get the best person if both sexes (a greater pool from which to select) are enthused enough to apply in the first place.
I won't argue that there are individual women that can outperform some individual men in certain fields. However, war is a team sport so we have to take into account how those men and women interact with one each other, all the side affects and extra costs that go along with a mixed gender force and determine whether or not it's worth it to get some women that are individually above average performers. If it's one thing we can't change it's human nature. And human nature is that men and women like to become romantically involved and sleep with each other. That causes all sorts of tension and disciplinary problems in units. There are cases of sexual harassment, abuse and assault all over the military. While these behaviors are abhorrent and should never be overlooked or downplayed, we shouldn't always take the easy and lazy way out of blaming men or a traditionally masculine culture for these problems. These problems will always exist in a mixed gender setting and there is simply zero ways around that because it's who we are as a species for better or worse. They exist in the business world just as much as it does in the military. The differences of course being that the stakes in the military are much higher and the military is taxpayer funded. Countries have a duty to provide the best military possible and a fiduciary responsibility to the taxpayer to do it as efficiently as possible. And then of course there are the additional issues of pregnancy, motherhood and the different general hygiene and medical needs of women that add an additional burden on the military and the taxpayer. Leadership and discipline are hard, they're very hard in fact. Should we make them even harder in the name of equality? Is that fair to the citizens we defend or to our young soldiers and leaders in the military?
For your point about diversity, I guess it depends if you think that good decisions help to win wars:
First, the Forbes article title is "Diversity+Inclusion+=Better Decision Making at Work" but when I click the link to the actual study I find that the study is actually titled "Inclusion+Diversity=Better Decision making at work." So either the author of the article is too stupid to even quote the title of the study he's reporting on correctly or, more likely, he's trying to push some sort of political angle by completely changing the title of the study. Either one is grounds for me to stop taking that reporter seriously.
Second, the study seems rather vague. It doesn't define for me what exactly they mean by "inclusion." Does that mean that superiors and subordinates meet together as a team to discuss possible courses of action and determine which one they think will lead to the most success? If so, stop the effing presses! That's groundbreaking stuff right there! I can't believe no one has ever thought of doing that before! Seriously though, the military has been doing that since the dawn of time and most businesses have been too. It's such an old and proven concept that it's really not even worth studying.
But even if I took the article at face value, which I don't obviously, decision making isn't the only thing that wins war. Discipline, esprit de corps, deployability, efficiency and readiness all factor in just as much if not more than "decision making," whatever that is defined as in a military sense. Do we sacrifice all those other things for the sake of one?