There are three basic ways that the mates determine wind speed and direction on ships equipped with an anemometer.
The new mate way,read the direction and speed off the instruments and then they enter the data into a computer program (Waypoint for Windows for example) that converts relative to true and they log that.
The experienced but lazy way is to just walk over to the compass and get speed and direction by observing the effects of the wind on the sea. Mates (or captains) don’t do it that way just because they have experience but because it quick, easy and accuracy usually doesn’t matter that much.
The third way, the experenced and careful way is to both read the anemomter and to verify visually.
What about at night? If the anemomter has proven accurate most mates in a routine situaton will just take the reading without much checking.
What about the case of at night no working anemometer? In my experenced they look to see what the last guy wrote down and write in the same thing or change it up a little if they think conditions have changed.
In the case of the El Faro this is where what was expected would have been important. If the last watch wrote down, say (for example) WxN F-7, next watch might think wind noise has increased so call it WxN F-8.
This is why an anemometer might have helped. For example it may have made the weather observation taken and logged by the mate more trustworthy and therefore most useful. The one hint that things were not right may have been that as they approached the center the wind direction would have been changing clockwise rather than the expected counter-clockwise. If you looked at what the last watch logged and it didn’t match what was expected the mate might figure the previous watch just made an error.
Better information would increase the probabilty that the true situation would have become known. I don’t see how that is in dispute. Of course if the crew thought that gettng the direction correct was important than likely they could have done it. But if they were confident they understood the situation there is no reason to they would have been concerned about it. People tend see what they expect to see.
It would be a tough argument to make in a courtroom, that the instrument used to measure wind speed and direction is of no help in that task and that the average mate will do just as well without one.