Whether it's sexist or not is beside the point. The point is what is best for the children.
I don't think it has to be all or nothing (all meaning 'in the circumstances' i.e. 50/50). There can be joint decision-making among divorced parents, wrt matters like medical care, education, extracurricular activities, etc., all discussed and agreed on, each parent can be aware of the children's schedules, and there can be plenty of phone, email, text or skype contact between the NRP and the children, alongside the usual residential parent/weekend practice.
It's up to the NRP to make the most of whatever opportunities they have to develop and maintain a relationship with their children. Some choose not to, which is sad because there are so many ways to keep in touch and be a presence in your child's life. Not the same situation, but my grandfather kept in touch with all of his siblings who had emigrated to Australia, whom he never saw again in RL, but they wrote to each other constantly. Shame there are people who do think a relationship with their own children is worth making an effort for.
The resident parent has to attend to the relationship too as the children grow. There are challenges for parents no matter what their circumstances. You have to put in the effort with children whether you see them every day or not.
A father who lives in the home with the mother and their children can have a very close or very distant relationship with the children, same goes for the mother. To that extent, I think Cameron has scapegoated absent fathers as distinct from neglectful parents in general.