Robatoy wrote:

Base-load power plants, like all others, can only generate the energy
that is consumed at that exact moment in time. You cannot, therefore,
waste output. You can, however, waste some efficiencies by running a
500 MW generator at 50 MW.

Yep. I didn't say the power was wasted, just the generating capacity.
(And as you say, some inefficiency is introduced.)

Since the capacity exists already, a certain amount of additional
off-peak power usage could be accommodated without any need to increase
generating capacity.

Chris