No argument there but methinks you are unaware how cheap and how reliable as baseload hydro is when the storage is full.
Kareeya once achieved 105% of rated capacity for a calendar month. Just one man in the control room, zero imports of fuel. [fourty years ago, still going strong]
Once water-levels drop they can cut back on the base load but they are there to respond to instant changes in load. At this time that control-room operator has to turn a knob as power usage varies, ie they have frequency control. he was so bored we used to talk at length.
When water levels dropped further they would reduce their daily output to peak only. Remember peaks occur both before and after the sun can be assumed to shine. Hydro is still there, doing the heavy lifting.
Eventually the water-level may drop to where it is only good for emergency, but they are never drained empty. But ALL these changes of priority are planned. The engineers use their slide rules so that there are ZERO surprises. There is plenty of time to tell steam driven stuff that they will need to provide more power in the next cycle.
Note also that the likelihood of a hydro turbine tripping out at the worst possible moment are far lower than other sources than, I assume, atomic power.
