So if both people in the relationship have the exact same job with the same pay. They come to a mutual decision that one of them will be the full time child carer for their children as it suits both parents over any other alternative.

Now the parent still working can further progress into their career earning progressively more money. They divorce 20 years after that decision and it is your opinion that because they didn't earn that money they are entitled to way less than their partner?

As somebody that works in law that is not equitable at all to me. You've made a joint decision to impact someone's career and future earnings for everyone's benefit and now they are being punished for it unduly.