I agree, it wouldn't be fair. But when I asked AI, it said even with 50/50, HMRC favours the status quo, especially if the party claiming CB has other benefits attached.
I wouldn't trust AI with anything like that. It's very American swayed with a lot of things.
A while back there was a poster convinced she should be allowed to claim PIP and Attendance allowance because AI said you could.
I wouldn't be surprised if it's conflating the family courts with HMrC.