You can’t argue with demographics, so you wouldn’t have argued with Malthus? He was completely wrong, at the very least in timescale.
Even if e.g. Korea somehow managed to get a fertility rate of 10 tomorrow, it would takes many decades for that generation to begin to contribute to the economy as a class of high-skilled laborers. No matter what Korea does, absent implausible levels of immigration, they are still set for future economic hardship due to their demographics.
America is quite unique in the world by being so significantly multicultural, and increasingly so. It can tune and balance its demographics with immigration. It is especially good at attracting the best and brightest from around the world, because there is a realistic, and well trodden path, of not only fully integrating yourself and your children into American society, but also integrating into the ruling/upper class.
For example, any Chinese citizen can effectively defect and build a safe and sustainable life in America. Millions have already done it. First generation immigrants lead some of America's most powerful corporations. Second generation immigrants are welcome as officials in the government. The current VP is second generation immigrant of Indian/Jamaican descent.
On the other hand, an American can never effectively defect to China. Maybe if you are ethnically Chinese, your children could be accepted, but not likely anyone else. China simply doesn't have a culture of fully integrating people of all kinds into it's society.
The funnel of exceptional humans is one way, and it's into America.
There's a comedian, I think Bill Burr, that says one of the great things about US sports is our incredible diversity. Look at any of our Olympic teams and you'll see all kinds of ethnicities in our teams, whoever is the best. On the other hand, I doubt you'll see the same on the chinese Olympic team. Obviously, there are other countries that do the same as us, but we do it on a pretty big scale and I think our success in medals is often in being comfortable with this. Heck, there are a few athletes that have the option of competing for us or their native land and they choose to go back to their country for that. Naomi Osaka comes to mind. She has lived in the US since she was 3 years old yet chose to play for Japan.
Does this idea also extend to ethnicity? This is far from the original topic, but if I emigrate to my wife's home country, I don't think I can ever say I am ethnically "Danish", (or can I?) but she has been "ethnically" American since the day they gave her an ID. Or perhaps there is no "American" ethnicity? I would love someone to educate me on this topic. Perhaps "American" ethnicity is represented in those who move here to be a participate in 'American values'?
To create a young person, you need a fixed number of years. If you want an 18 year old to hit college and take on a $100k loan (or join your army and shoot your enemies), you will have to have started in 2004. There is no way to accelerate this.
Even if you poured all your energy and resources into getting people to reproduce more starting today, you won't see an active worker or soldier or college student/scholar until 2040.
What happens in the interim 18 years?
Isn't that also a problem with the "refutations" of him? They're also based on history, just slightly more recent history. It's quite possible that future "advances in food production" will eventually fail to keep up with (perhaps slower) population growth, or future changes (climate change, reductions in fossil fuels, etc.) will undo some of the previous "advances in food production" required to sustain our current population.
You hit the nail on the head. Most people who say Malthus is wrong are refuting a strawman that has nothing to do with the original strong argument.