Seems you have made a big mistake, and now the CMS system and HMRC are involved, whereas before you could have just continued to get on nicely enough and probably left things as they were.
If you have 50-50, there really is no primary carer.
Because the system can't easily tell whether you actually are 50-50, they use who receives child benefit as a simple way to tell who is doing more of the parenting than the other. But it's really a secondary way of measuring things - a quick and dirty substitute for the actual truth because that's harder to figure out.
HMRC will quite commonly award a child benefit to each parent when there are 2 children, so now he and you are basically completely equal in terms of what CMS looks for. So neither of your will get CMS from the other.
What part do you think is unfair? He earns more money, and presumably spends more during his 50%. You have the option of going and earning more money too.