Women and sex

 But can they not do at least most of the things men can do?

They can ... just not as well.

Do women have to do a task better than men on average for there to be women who are productive in some way? 

Yes, otherwise I would replace them with a man.

There are female inventors, female therapists, female office workers, etc. 

Female inventors are maybe 5% of inventors. Men make better therapists than women, but they're less interested in such emotional jobs; women get the leftovers. Men work at the office better; they're less likely to file HR complaints.

Due to individual comparative advantage (i.e. different people being good at different things), it's not like you can just replace any women in any role with a man

With every useful task out there, every man is better than every woman if they put in equal effort. Some women are better at math than me because they put in way more effort. But take any woman out there, she will be worse than math than me if we put equal effort into the subject. Testosterone is for power; estrogen is for aestetics.

 If you go to the restaurant and you get a waitress, are you gonna leave or demand a male server?

I don't eat at restaurants because of the price; but women do a better job here because they look better. A woman chef makes one meal for her family. A male chef makes hundreds of meals for strangers. Maybe one is better than the other per meal, but chefs make more meals than housewives because the work environment stresses out the highly estrogenated.

In all other ways they are equal.

That's fake. Men are better at every skill than women if the effort and dedication to said skill is equal.

What % of astronauts have been women in history? Exactly. You can find women willing to undergo the stress to become an astronaut, but they're very rare.

Such women are the exception; women astronauts are not normal; they're rare for a reason.

There are women making progress on unsolved math problems and winning Olympiads. I think it's unlikely you or most men could make the same progress as the top women with equal effort.

Such women put more effort into math than either one of us did. They have PhDs in math. Getting a PhD requires immense effort.

The smartest women is not dumber than the dumbest man, if that's what you're implying. If you really want to defend that then we can debate it but it seems so obviously false I'm gonna assume I'm somehow misunderstanding your point.

You misunderstood and that's fine. The smartest woman in the world puts way more effort into her intelligence than the dumbest man in the world, but she's dumber than any man who puts equal effort into his intelligence as she did for hers.

men have a finite amount of time to learn tasks, so women can always find some job the man isn't doing. 

Yes ... the women do easier jobs for less pay. You think sweatshops were the normal job in the 1920s? No. Sweatshops were a woman's job then. Now, those jobs are largely automated in the US.

And they have a pretty big incentive to make money however they can.

Cheap labor.

If being a member of a below average group made someone not useful, then the vast majority of people would not be useful since they're in the group of "not the smartest or strongest person in the world."

People are useful even if they're below average, but men are more useful than women. A quarter and a nickel have different values, but you'd take both. But you'd rather have 2 quarters than 2 nickels if you can only get 2 coins and if you can get more, then you'd want all the coins to be Quarters. In the 1920s, the Quarters worked non sweatshop jobs.

Are you arguing women being useful aside from making kids is rare or that it never happens?

I'm saying women being useful aside from making kids is less common than for men. A woman can be useful, but it's more common a man is useful than a woman is (aside from making kids).