well I always said Marvin was great. But if he thought he could beat Spinks he would have moved up and fought him. I don't think he wanted to fight him. He knew his advantages would be diminished and he might be there against the Spinks Jinx. Hearns had a right hand, but Marvin relied on the fact he was a solid middleweight to take Hearns punch and then put the pressure on Tommy, With Spinks there is no way he could put pressure on him like that. The tables would be turned. He always demanded Duran,Hearns and Leonard move up and fight him as he said the legends, so I think he should have tested himself like they were tested. And that doesn't mean I think Marvin is less of a fighter, but moving up does prove something. Takes away certain advantages where skills are more the variables.
To be fair I don't think the demand for the fight was ever there. I don't recall it ever being discussed in the trade press or amongst informed fight fans(plenty around then!)