Are you actually asserting that demand is level 24 hours a day?
It can come very close.
In California, for example, a very large part of the demand is pumping water through aquaducts. By placing reservoirs along the way and doing most of the pumping during times of low electrical demand, California electrical utilities used to be able to keep the power demand nearly constant - and can still keep it much more level than in many other places.
Also: Coal plants can provide baseload, while wind and solar together do a great job of shaving peaks: Higher wind corresponds to higher HVAC load as well as higher generation. Solar not only tracks the air conditioning requirements but also comes close to tracking the daily load peaking - and solar plus wind tracks it even better, since the lake effect makes an afternoon-through-evening hump in wind generation.
at a power output proportional to the CUBE of the windspeed.
is this relevant somehow?
Yes, very. The steeply up-bending curve means that wind generators that are able to make use of high winds - which only happen for a tiny fraction of the time - have a peak power rating far above the average power they are able to produce in normal winds. So the peak power vastly overstates their average contribution.