It does seem an odd situation whereby people are asking if a second ATC controller, positioned at the side of an approach, at night, could have a better visual appreciation that a 2 man crew could be lined up, visually, on to the wrong runway.
It's about providing additional layers of safety.
When pilots make errors, we want to give controllers the best chance to detect them so corrections can be made. Likewise when controllers make errors, pilots should also have the awareness and tools to detect and correct them.
I find it odd that the layered approach to safety is so difficult for many to understand. The 'Swiss cheese' model has been around for awhile now.