If it's the same Joyce that got in the ring with Parker, he wins. Joyce will actively cut the ring, close escape routes, and unload with mean intentions for whatever the distance, each and every moment of the round. The style difference that resulted in Parker losing to Joe, but winning against Wilder and Zhang is jarring. Those are entirely different realities of combat.
I said about Joyce for a while that he has been a long time past his best. His absolute peak was against Dubois but he's steadily declined since then. His power is a great equaliser but I really do think his days at the top are finished. Him v Parker is a great fight to make.
Roided Joyce beats Parker 9 times out of 10. Parker struggles when he gets a pace set on him and he can't deter an opponents walking at him.