Most of it is, but not all of it. My own conclusion (which is not the one I wanted to reach, believe me) was that when you throw out all the bad research, the evidence, while not conclusive, does clearly point more in one direction than the other.
This post mentions a few of the main ones (I'm not vouching for the post's content): https://www.laleche.org.uk/letting-babies-cry-facts-behind-s...