It was:
1) A better engineered boat
2) A better engineered sail plan (wing and soft sails)
3) A better team effort to understand how to sail their boat in various conditions and points of sail and transitions

A5 failed on those points, came closest on #1, their sail plan, even given the soft sails was not well though out.

And, like John says, truly back to the roots of the Cup IMO.