Oakmaiden
PR is not hard to get - easy, in fact, if mother and father agree - they just sign an agreement. If the mother disagrees, then, like your contact, the father has to apply to the court for a PR order.
As with ALL LAW governing the welfare of children, the 1989 Children's Act comes into play, which says that the best interests of the child need to be paramount in any decision.
Research into the role of fathers in child development and welfare is very clear - in the vast majority of cases (i.e. excluding alcoholic or abusive fathers), the involvement of a father in their children's lives will have a significant impact on that child's cognitive, social, educational and physical development. So it's hardly surprising that PR orders are granted.
The governing principle of the law is the best interest of the child, not the wishes of the mother (or father), in spite of how often these can become confused.
I think you may be right about the politics - the judge was put in the position of assertaining the best interests of the child - vaccine or no vaccine - and there would have been political hell to pay if he'd gone for the non-MMR vaccines.
Your transferable idea is OK, but in all European countries where leave has been transferable, it is the child's relationship with the father that suffers, as the couples tend to chose the mother to take the leave. We still have a ridiculous pay gap between men and women here in the UK, and I'm afraid that would be the case here. Only when it's non-transferable do children not lose out on their dads.