It's difficult to quantify exactly how much human population has really grown. It's estimated that the Black Plague took 20 to 25 million lives which was thought to be anywhere from 30% to 50% of global human population at the time, which was between 1348 to 1350. The estimated population in the 1600's is roughly 500,000,000 (five hundred million humans). Roughly half of the population just 200 years later by the 1800's, where we reached 1 billion people on the planet.

So in just over 200 years we have expanded 7 fold. Even adding up the entirety of the human population from 5,000 bce to 1100 A.D. is barely reaching the total amount of humans we have today.

For context, we're at/near 8 billion now. A century ago, 1923, we had roughly 2 billion people.

The sheer amount of expansion we've had far outweighs total lives in human history. Multiple, multiple centuries of humans never even came close to amounting the resource draw which we have today - in part due to technology, in part because we've paved a way for more efficient destruction, and in part because we have multiplied our numbers.

I don't intend to imply that groundwater extraction should cease, only that this effect desperately needs to be studied further. Perhaps we can develop a way to safely replace or counterbalance the mass of the groundwater we take out. Perhaps we wont need to, and natural processes that take longer than human timescales will have negative feedback mechanisms that will gradually counteract the effect. We need more precise data than an 2 decades model can provide if we want to be able to project how this will continue. Of course we also don't want Antarctica at the equator in X thousand years. We should understand what's happening better before we define and label this as a problem problem develop and propose solutions. But the known unknown, the potential for extreme axial drift leading to mass exctinction via a "global roll," is just waiting to be investigated.

Haven’t humans been extracting groundwater (i.e. drilling wells for drinking water & irrigation) since prehistoric times?

Most of the time limited by their own muscle power. Then a few animals. Then steam engines and motors with potentially unlimited power.

Right, but we've seen effectively exponential population growth in the last few centuries. Global population just 200 years ago was 1.2 billion, and those people had far less industry needing groundwater for their processes.