If you're at higher latitudes, this is notably less of a drop-off than you see between high/low season.
My friends with residential solar see <10% overall output in January vs July. (~60% drop from fewer sunshine hours, ~80% drop from decreased solar irradiance.)
Many pure-numbers theoretical comparisons also make the assumption that you can consume all the power that the cells generate, which is not always the case. In an off-grid installation with a battery, for example, you might not be able to consume everything, depending on the month of the year. Practical example: my installation gets some of peak usage numbers in March/April, because that's when it's still cold and I use the power for heating. The cells are cold, I need the power, and there is some sunshine, all this combines. It's not obvious.
This argument is almost closed at this point, with PV + batteries being quite price competitive. We're no longer in 2018.