That's not how the world is.
It's not necessarily true when you compare between organizations, where different groups may make subtly different decisions with wildly different outcomes (although even then, a lot of the difference comes from different circumstances and not innate talent of the people involved). But in an organization, the need for teamwork and to "row in a common direction" tends to flatten out individual differences, and there're generally two possible classes: "valued contributor" and "holding back the group".
(This is also why large organizations like Google tweak their hiring processes to avoid false positives more than false negatives. One bad hire forces the team down to his level, as they always have to stop and explain things to him, or he'll block them from implementing a cleverer solution that he wouldn't understand. One good hire, however, very rarely raises the level of the team - he needs a lot of patience and very good empathetic & people skills to do so.)
No, that is simply not true. There might be a cutoff over which everyone is "reasonably competent", and perform "acceptably", but there are still huge differences between people.
You immediately say "no" to people that don't reach the "acceptable" bar. But above that, you have hiring quotas, and you try to maximize the value of the people you hire. Hiring someone just above the bar now means you get one less hire later. Someone much better might show up, and often does. And on the other hand if the current candidate is much, much above the bar - you fight to get that person hired, you work on convincing your peers in the hiring process. Because they are worth it. Such people have a much higher chance to be hired.
I've been on both sides of the hiring process many times and worked for many years in tech. To say that above some skill level everyone is the same, "can do it as well as any other" - not in all of my experience.
(FWIW, I would pay much more attention to individual performance differences if I were hiring for my own startup than I would when interviewing for Google. But I thought the context of this discussion was organizations large enough for gender quotas to matter, i.e. the Microsofts and Googles of this world. If it were my own startup, I'd try to hire from the population I've personally worked with, avoiding this whole discussion anyway. And I have never worked in an organization with a hiring quota - the companies I've worked for will all take you if you meet the hiring bar, and hold cash in reserve so they can scoop up a suitably-qualified employee if one presents herself. For that matter, I've been given offers at several places that were "not hiring", so I'm guessing quotas are just guidelines in many other places as well.)
