I didn't read the articles so hopefully my answer is still helpful.
I teach elbows about halfway between down and back - where exactly will vary a bit on a lifter's anatomy. This is allows the proper/ideal scapular position to create a stable base, allows a good hand/wrist position, doesn't place the shoulder joint into any problematic position, and helps the elbow joint support the weight well.
Having straight down or straight back is problematic each for its own reasons. My guess is that if anyone is actually saying straight back, it's a translation problem or miscommunication/misunderstanding.