It’s a shame that your ex is unwilling to be part of your DC’s life ☹️ but yes, I believe 50/50 is best for children (caveats below) and this is supported by academic research.
If all avenues have been explored eg, talking about what it could look like, mediation with a family mediator to help talk about it etc; then in your situation, at this time, it’s easier and better for you to not be 50/50. Time will tell if it affects your DC in the future in terms of outcomes (educational, psychological, relationship, confidence, self esteem).
I have experience of being brought up in a household whereby my dad couldn’t be bothered either. He had his new girlfriend (who he later married) and him seeing us was a tickbox and emotionally he was unavailable.
Hindsight is great isn’t it as my view now, dealing with what that relationship did to me in adulthood (feeling of abandonment, choices I made in my relationship based on how my dad treated me and my mum) wasn’t great. In a way, I wish he wasn’t in my life at all. Back in the 1980’s it was encouraged to see your dad EOW because “he’s your dad”. I personally think that was wrong advice as he wasn’t interested, nor was he a good dad, he was a sperm donor; and that was known and clear by me from a very early age (around 7 years old).
Depending on what you’re measuring as outcomes, for example educational/ career, I was successful in my own right. The feelings of abandonment put me in a position to be the best at school and then in the workplace (perfectionist, people pleaser). But if we’re measuring physiological outcomes, the set up only seeing my dad EOW was damaging for my relationships, choice of man I chose to have a child with, and the whole people pleasing thing was because of the love I didn’t get from my dad (I’ve been therapy, can you tell?!)
I should have been nearer 50/50 with mum and dad, or not seen my dad at all.
My DD is currently thriving from 50/50 set up. It will be interesting to see how she is as she moves into adulthood. We talk a lot and she’s very bright and emotionally intelligent (which helps). I genuinely believe if she saw me or her dad less than 50/50, she’d be really conflicted. With her being an only child, she has no divided loyalty with either of us. She loves us both equally and enjoys both our company.
Look, as per my previous posts, there are so many nuances to if 50/50 would work or not. The main ones being how capable the other parent is, how much the normal caregiver is willing to let go of some of the things that aren’t their way of parenting, and most significantly, age of the children. Research suggests that younger children do benefit from having a base home, one carer, with visits to the other parent, as opposed to 50/50. The increase visits/overnights as they get older.