Not saying he is better. In fact, he is worse.
But they can be compared from JR's 1st year to Skeltons 2nd & 3rd year. Sanders has a great thread on expected improvement from JR.
How can you compare a rookie to a 3rd year pro? Those were Skeltons 1st & 2nd year stats. It was worse than JR's plain & simple. You can take Skeltons first 13 games & still have worse stats. In no way, shape, or form was it better than Rosens.