You would forget that this would cause exponential growth: in a couple decades, a single lab could produce more people seeking tenure track than an entire count

You would forget that this would cause exponential growth: in a couple decades, a single lab could produce more people seeking tenure track than an entire country's worth of positions; there need to be smarter ways to provide the requisite labor for science, since this is clearly unsustainable praxis. Running a pyramid scheme of this magnitude is only going to cause an implosion—which we may already be witnessing.