Earlier quoted context omitted.
Without economic growth we’d still be hunter gatherers. Growing crops allowed people to have excess food and support classes of people whose occupation was non-food related. The industrial revolution not only allowed for mass production but the Haber process by which fossil fuels are turned into fertilizer. Without it we would only be able to feed half the world.
Technological advancement and human overpopulation are orthogonal concepts. It’s perfectly reasonable to believe the planet is heavily overpopulated with humans and also that technological advancement is desireable. There is very much not a direct relationship between absolute number of humans, and technological advancement. This is increasingly true as we inch closer to AGI.
There very much absolutely is a direct and bidirectional link between the two. Technological advancement (esp fetilizers) has been crucial to the increase in the absolute number of humans to its current level.
There is also good reason to think that there are direct effects in the opposite direction. There seems likely to be a minimum population that can support the degree of specialization needed for a given level of technological advancement.
But while there absolutely is a direct relationship, I don't think that your core point is necessarily wrong. The minimum population required to maintain our current level of technology might well be one or more magnitudes less than our current population. Our current population may well be sufficient to achieve the level of technology required to become a space habitating species.