Basically, literally all the people I know who are divorced with children are going through some horrible shit re co-parenting. A few friends/ family members I know who dated divorced dads ended breaking up apparently successful relationships because they couldn't handle the constant presence of the mother / constant change of plans / always needing to be in touch over the kids. My closest friend is a divorced mother of two and she jokes, ("jokes") that the amount of time she and the father of the children spend arguing and on the phone with each other is more than the time he spends with his OW. And they are still in and out of family court SEVEN years after their divorce.
I am undergoing divorce. In my case, the father of my two children has buggered off to another country. Although I feel abandoned and horrified by the responsibility of bringing my kids up by myself, I have other people tell me "you are so lucky!!" b/c the father is out of the picture. I don't feel lucky AT ALL!
Maybe I just know unusually acrimonious bitter people, and "amicable co-parenting" isn't in fact a myth?
My older brother is my half brother, and his mother and my DF/DM made it work brilliantly. It meant pulling together when DB got stroppy or said he wasn't going to stay with/see one or the other, and it meant all parties working hard to be amicable, but it paid off in spades. His DM always sent me and my younger DB presents for birthdays and Christmas, and we saw her for a family lunch at Easter, where she had brought presents for my DD as well as DB's kids.
Ex and I split over 10 years ago when DS1 was 5 months. It was awful initially; he was in self-destruct mode and introduced several flings to DS1 whenever he had contact, drank whenever he had contact, would return him late and we were both hateful for a while. I wasn't perfect either; I used to try to refuse to allow contact unless he danced to my tune, thinking my choices and opinions were more valid than his, and that I had a say in how he chose to parent DS1.
We grew up. We met other people. We started to sort ourselves out and realised that our attitudes to one another were going to have a huge impact on DS1. He's 11 and a half now and Ex and I get on well enough to spend days out together. He comes here at Christmas with his DP and her DS. He is as big a part of DS1's life as I am, his DP is kind and loving to DS1, I have remained in contact with his parents and sister so that DS1 hasn't missed out on contact as he's grown up.
It's entirely possible to co-parent successfully. At the immediate end of a relationship feelings and egos are bruised; very few people can behave flawlessly when hurting. But long-term it's possible. Both parties have to be willing to behave respectfully and kindly, both parties have to let go of all the shitty resentment and ill-feeling. Both parties have to accept their share of the previous shitty shenanigans. Both parties have to put their DC first. If those things happen, co-parenting is fabulous.
As an aside, we never went to court. We never had a formal agreement. We never dragged it out. We agreed (after the first few months) that we'd play it by ear and try to be flexible with one another. It's worked well for us.