Sure, but less grain is often worth it. There's a reason why fast lenses exist. The high quality lens being used here can probably still resolve 20 MP adequately even wide open.
replyI had that lens. It’s soft as fuck around the edges open.
replyPeak sharpness is about f/8. They should have had the D5 on aperture priority auto iso, pushed the exposure comp either way and then just fired at f/8 and let the camera make the decisions.
But they are astronauts not photographers :)
The modern Z lenses are far better and sharper open but much larger generally.