I think you guys need to relax and give credit where it's due - Slater won the Grand Final, not Hayne. As a winner, he deserves the number one jersey.
Also, take a closer look at the Grand Final - whilst neither fullback was at their explosive best, every time Hayne looked like making a line-break or breaking a tackle Slater was there to stop him.
Billy Slater deserves to play fullback for Australia. Especially seeing as he plays better at fullback than on the wing, but Hayne can play wing pretty well.