I like Spinks's adaptablity, awkward herky-jerky style, and very effective jab to win a decision or maybe stop Jones late with the dreaded "Spinks Jinx". Spinks's right hand, though, wasn't his only devastating punch. Ask Marvin Johnson.
Spinks' rangy and aakward style, with his effective jab would present a lot of problems for Jones. He had a good arsenal of shots, highlighted by that brutal right hand. Spinks would probably stop Jones late, if not, his style suits him more against Jones than RJJ's suits him against Spinks and Michael wins the decision. Roy has to be superior on the outside to win, against Spinks that may not be the case.
Proevoyoda. Are you comparing Duran getting KO'd by Hearns to Jones getting KO'd by Tarver or Johnson? Duran was a natural Lightweight and past his prime despite going to beat Barkley five years later. Jones fought Tarver three times, all near his natural weight class of 168 (7 pounds extra). Who has Tarver KO'd since that was decent? Johnson has had one KO in ten years and it was against Jones. He ain't a big hitter, Hearns was.