One partial solution to the renewables problem is to massively over-build. If they continue to drop in price, that will be feasible. Solar can be built up to the point where it will reliably produce sufficient daytime power even on very cloudy days for instance. Obviously it doesn't produce at night, but usage is also lower at night (in the future variable pricing to keep that the case as more electric cars come online). Likewise wind turbines can reliably produce power day and night if they're a bit geographically distributed and in sufficient numbers. This also means that often there will be more power available than needed. Some turbines can simply be stopped (braked) during those periods, but we may indeed find many loads can be time-shifted, reducing the baseline amount that needs to be reliably produced.

Long way of saying I agree with you; to make a reasonable comparison, you need to include an over-building factor to account for the variable nature of renewables. I'm not sure what that factor is (obviously it depends on a lot of variables), but I know it's been studied.