That's a fair point. Making matters more complex, adding more intermittent renewable calacrity added to the mix reduces the utilization of fossil fuel. Renewables have no marginal cost, so they can go all the way down to $0/MWh (and below!) on the spot market. NG is more dispatchable than coal. So it is in a better position to tolerate real time competition with wind and solar. The economics of coal are becoming increasingly poor because it is losing so much utilization. At least in the US almost all new capacity is wind, solar and NG.
Ironically, inclusion of battery storage into the grid will not only help wind and solar, but may also help coal and nuclear. Batteries will smooth out the intermittency of wind and solar, while smoothing out the intermittency of demand making it more conformable to base load generation. Any home with solar that charges the battery during peak sunshine and late at night when grid rates are low is actually helping all both extremes. However, depriving coal and nuclear access to the peak power rates that occur when the sun shines brightest will undermine the profitability of baseload power. So while batteries can help with utilization it will put a cap on peak rates. So either way coal is doomed.
The virtue of batteries is that they enable the cheapest marginal producers of energy to optimize their utilization. Batteries will squeeze out the peakers. So this will reduce the total capacity grids require. This is potentially more threatening to utilities than wind and solar. Because utilities make money on their total capacity and recapture the investment from ratepayers. So as capacity requirements decrease, both the size of their asset portfolio shrinks and many assets lose value. The utility industry could be headed into a massive asset bubble. Will they be able to pass these capital losses onto ratepayers? Maybe not, if enough ratepayers defect by throwing up rooftop solar and rounding it out with batteries. This is what I find so fascinating about home storage, it will empower consumers with choices that transform them from being mere ratepayers to being customers who must be won over with superior service and prices.