Papers are great, but the fact that this is still a topic of discussion in the 21st century shows that there are no magic bullets, and putting too much stock in a techniques can feel as bad as the problem you are trying to solve if they don't work and you blame yourself.
Among any parenting peer group there will be some whose children fall asleep instantly with no intervention and some who spend hours doing bedtime and get woken up dozens of times a night, despite doing more or less the same thing.
Very much this. I do like that they split the children into "crying-start", "alert-start" and "asleep-start" groups, but ultimately I have had the experience that every kid is different and sleeps differently.
Among any parenting peer group there will be some whose children fall asleep instantly with no intervention and some who spend hours doing bedtime and get woken up dozens of times a night, despite doing more or less the same thing.