Right, we could definitely have real productivity growth without population growth - that's increased efficiency (I doubt this is possible without increasing energy expenditure though).

I think the problem is still the one I pointed out, whereby if increased efficiency halved the number of man-hours required to make an iPhone 15, instead of "being happy with the current iPhone 15 for half the cost", AAPL/the market/people's demands would result in the same number of man-hours being utilized to produce the next fancier iPhone 20 (or VR headset).

So I think a significant cultural shift would be required for increased productivity to translate into less work, rather than "more/better stuff" for the same (or an increased) amount of work.