All Dexter needs is to display his ribcage depth, work on his calves and perhaps some thickness in his back.
He has the shoulders and the abs but you need calves too to frame the physique and so he ought to spend the whole year just working those things. He DOESN'T need more overall size, after all, he did win the Olmypia at his current weight.
It seems strange to say but because of Jay's claves, you could say that Jay is more balanced than Dexter. Dexter needs to come in sliced to the bone, make sure his tan and oil are right, display his ribcage depth and get those calves up.