I think the key provision here is the paramountcy provision, which is an enforceable provision in the legislation. I think the purpose clause, and in turn the preamble, provide more clarity. Not being a lawyer, I can't speak for the Department of Justice on that issue before the courts, but that is the intent. It is that a preamble and a purpose clause provide clarity, and then the paramountcy clause is the specific provision that really matters in this case.
On November 17th, 2016. See this statement in context.