Open cycle gas turbines (which normally would be used to balance the grid when there's no sufficient renewable generation capacity available) operate at around 30 - 40% efficiency. At low temperatures heat pumps lose efficiency too. It can turn out worse than burning natural gas directly for heating.
It is not just about production of electricity but its use. It is about efficiency of electricity at consumer level. Heat pumps that use electricity are way more efficient than 100% in producing heat because they use the heat in the air and no boiler or heating element can compete with a heat pump even if it is 98% efficient. So the electrical grid can provide more efficient heating only if people use heat pumps. This is about efficiency of electric grid and not the source of the electric power generation. This obsession against renewables is political and it has nothing to do with electrification and the grid.