Let's forget for a moment that the economic system is there to support the people, rather than the other way around. Before the industrial revolution energy was usually the thing in chronic short supply, and wages were driven to the floor. Since then the thing in short supply has usually been skill-weighted labour, and energy prices have been driven to the floor: $10/bbl oil is a recent memory. We're not short of energy yet, but we do have the wrong infrastructure as we change energy input, and it is a big job to replace our oil-dependant transport infrastructure (and/or start producing diesel/petrol artificially from other energy). In summary: labour productivity is not always the most important issue for growth (positive or negative), and currently it is nearly irrelevant.

Another thing to understand with respect to productivity is that it is often concentrated in a small number of workers but spreads. Consider barbers. The cost of a haircut has gone up in line with general wage levels. If it didn't there'd be no barbers: they'd all go off to more lucrative employment. Yet clearly a haircut hasn't changed. Yet people who look at "labour productivity" reckon Barber productivity must have gone up. I believe this "barber effect" is the source of most wage rises. Or look at the other side. Suppose we are trying to work out the EROEI (energy return on energy invested) of some energy source. The energy workers get paid, and that money is used for energy, which might reasonably be included in the Energy Invested. We can't afford EROEI to fall below 1 (indeed we need much more), and one way to improve the EROEI is to reduce wages to energy workers. However note that this can only be done in the context of all wages falling, otherwise the energy workers will leave. So in some way the need to reduce energy worker wages will have to happen in a way that transmits to all society. Sometimes you can see that something will have to happen even though you can't predict the mechanism, but understanding will be deeper if we understand the mechanism.