This is too deep to even try to put it into the equality box.
Some parents just are not fit to be parents and can damage the life of a child.
Children also need both parents for growth and discussions about life, they need a Father figure at the worse scenario and or a Mother figure.
Each situation in my opinion still needs to be looked at. It shouldn't be a simple case of equal share in every single case.
In addition, I do loathe Mothers that attempt to gain full custody to get rid of that "man" that was once in her life and has no consideration of the child what so ever or has moved on with another Man who she "prefers" to be the role model purely out of her own selfish reasons.
But, having said that. Some men fight purely due to the loss of finances so that he can have a point of winning and then does nothing for his child/children when he has custody.
So again, each case should be looked at.
In a good World. Each parent acknowledges that this is about the child only and not them.. If only that would be 100% of the time.
Therefore in my opinion, shared custody is not obvious. The whole reason why Mother's were viewed as having an important role is obvious. Dated back, she predominately was a stay at home Mum, therefore the level of concentration was high, with helping with homework, when a child needed to speak and be heard, understood, helped and the Father being the bread winner, for the most part was too tired to listen.
There is also an obvious fact that women are nurturing, have intuition and perhaps more easier for a girl at least to discuss becoming a woman with.
I do believe that a child needs both parents.
But, I do believe that what's best for the child is the issue, in some cases, it is best for the child to be at home with it's Mother a bit longer than across at Dad's house not doing homework