But gas is used also in the summer. And energy is not only electricity - heating is currently done mostly by natural gas, and is often absent from those calculations.

Efficiency is irrelevant. The only thing that matter is cost and feasibility. The cost of energy from solar is ~$0.02/kwh and sometimes even $0.00/kwh (when the grid curtails production). Even with 30% efficiency each kwh retrieved from storage will cost a record-low of $0.06/kwh (3-10 times lower than the consumer price).

The biggest factor here is the capex and ease-of-use of the equipment. Not the energy input cost.