Your definition of efficient doesn't make any sense. If people can work less and produce more, that is the definition of efficient.

I agree that keeping everyone fed and sheltered is of primary importance... but wouldn't it be better to have everyone work less while doing that?

Let's have robots do all the hard work and then share the wealth with everyone. Why force people to work at jobs that could be done easier just to make sure we employee everyone? Might as well just pay people to move rocks back and forth.

Just increase taxes on robots and use that to pay basic income.

A carpenter using a hand saw instead of a power saw just to keep more carpenters employed is not being efficient. It's Pareto-better to keep all those carpenters employed, earning the same salary for fewer hours.