It might very well happen to China but I don't think this is an inevitability or 'math'. Diminishing returns appear when existing systems are pushed towards the

It might very well happen to China but I don't think this is an inevitability or 'math'. Diminishing returns appear when existing systems are pushed towards their limitations, but it doesn't account for the dynamic nature of technological progress. When we were plowing fields with horses there were diminish returns but that didn't imply the end of history. You invent the motor and you're in an entirely new world altogether. Through paradigm shifts you can always reset the timer on your returns. And sure we might be in an era of stagnation for 100 years and all the singularity people may be crazy but how likely is it really, that in the grand scheme of things there's not another era of rapid change, and that some country in principle can find a mode of governance that doesn't end in 'late stage Japan'?