Again, the letter makes sense, especially given the point she is trying to make--and it is more persuasive--if she shows us who Scott was before showing us who Scott became.
Otherwise, I read that and I think, 'Why did you marry and have kids with that loser douchebag in the first place? How dumb are you?' Since we know from other perspectives that sober Scott was a good guy, then the letter comes off as a list of examples saying, 'Look how fucked up this guy was and what a shitty father he was," as opposed to a cautionary tale about abuse and fatherhood. It's NOT the same cautionary tale if Scott was fucked up and shitty the whole time, including when Mary decided to marry and have kids with him. Then it is a cautionary tale about being careful about who you marry. And that's not the point she was making.
While I am inclined to believe most of what she said (the Christmas/atheism thing makes no sense), I actually resist based upon the fact that it is just a list of shitty things he did without a frame of reference telling me if he was ever not shitty. So I am also inclined to believe that this was an opportunity to tarnish him, and she did it under the guise of a cautionary tale.
Because of that, I look at things she said much more critically. Like, how and when was CPS involved? Only recently? Years ago? Just once? Scott hasn't seen the kids in years? Why exactly? Did you move away? Is he constantly touring to pay you your alimony and child support? Has he tried to see them? Did you do your best to block his requests, which may have had to squeeze into his work schedule?
Again, I am inclined to believe he slid into being a bad parent, but I am also inclined to look at it critically with the way she chose to tell the story.