What is more unsustainable, IMO, is the concentration of work. 3 out of 10 men and 4 out of 10 women over 20 year's age in the US are not working. Working far in excess of 40 hours per week is common. US vacation is still generally a paltry 2 weeks, non-mandatory.
And all this, despite continual improvements in productivity over the past century.
Couldn't we collectively reduce our working hours, have more vacation time, and employ more people? That would more fairly disperse the productivity gains of technology and improve many people's lives.