Can you not vent some of the steam, so the same volume of steam is being produced and the temperature the same but only some of it goes to the drive?
Can you not vent some of the steam, so the same volume of steam is being produced and the temperature the same but only some of it goes to the drive?
The comment was about the ability to vary power at all, not doing it efficiently.
Are you going to choose to crash into something because it's wasting fuel to vent part of the steam?
The ship command structure was a form of information hiding, whereby the commander only worried about the speed, whilst the engineer worried about how to efficiently deliver the requested speed.
Under emergency you will vent, but under normal operations where you just want to slow down you care very much about efficiency.
Not just for monetary reasons either (though that's a factor) but because the lumps of coal you're not burning now could save your ass in bad weather and make you reach safety instead of being stranded in the middle of the ocean.