The planet and its resources has a finite carrying capacity. Given we have most of the world in need of developing to reach the levels we enjoy, I suspect we are far past that capacity already -- though I am unlikely to live to see the consequences of that. We've used the world's most fertile land already. We've had the fossil fuel fertiliser dividend. Do we continue to grow and pretend growth is normal and necessary until we absolutely need another agriculture miracle? Or do we try and construct a future where everyone has a chance of abundance?
Even claiming innovation is partly a function of population size is far too simplistic - we've had periods where small countries were punching orders of magnitude above their population weight. There'll be little innovation if the food supply breaks.