Motors efficiency, an generators efficiency, can easily be 0.95, and even 0.98.

So overall the lift approach must be pretty efficient, even when we subtract losses for friction in the rope and of the air.

The energy density isn't great, though, you need really much mass, and large elevations, to store anything interesting.

Pumping large amounts of water uphill is more feasible, even if less efficient, and is actually done.