Same day weigh in makes it tricky, but I believe Roy has the foot and hand speed to decision Conn in a competitive fight
Yeah Conn was amazing and one of my favourites. But its hard to beat Roy unless you can either hit like Bob Foster or outspeed him. Conn is quick and has the fundamental skills to make it competitive but RJJ is just too quick. RJJ also has more power so even though he isn't knocking Conn out, RJJ will land the occasional combo to stagger Conn and this will score huge with the judges.
Jones would be a corpse as a 168lbs same day weight in, even if we’re taking the 160lbs Jones, he was rehydrating to probably mid 170s. Billy Conn, by some accounts, was like 168lbs or so against Louis and actually officially weighed like 170lbs in some fights, he may struggle to make 168lbs on a same day weigh in, but he wouldn’t be a corpse.
To have a chance against Jones you have to be able to punch. Jones is too fast for almost anyone you match him against. Jones by a clear decision.