With regards to 'economic advantage', the advantage has to outgrow the overall growth for the state of carbon originals to decline.

There is no reason why this would be true. The economy can grow enormously while per-capita income and standard of living fall. This has happened before, the global economy and population grew enormously after the transition to agriculture, but living standards probably actually fell, and farmers were shorter, poorer, harder-working and more malnourished than their forager ancestors. It is not inevitable (or even very likely, IMO) that the economy will perpetually outgrow population.

Also, you may want to read Accelerando by Charles Stross.

I read it years ago, and wasn't impressed. Why is that relevant?