For what it's worth regarding Greb/Langford I have an OLOd Ring Mag where a reader asked Nat Fleischer [who saw THEM ALL] this question...What round would Sam Langford catch up and ko Harry Greb ? Nat Fleishers answer was " I dont believe Langford or anyone else his weight would have ever caught up with Greb "... For what it's worth....Harry was perpetual motion,difficult to time... Like a Knuckle ball...Pardon the pun.....
Greb, Tunney and Loughran all had what it took to stay away, survive when in trouble, and take a decision. I feel less confident about Tommy than Harry or Gene, as Lomski gave him some serious problems early. Qawi is a stylistic counter punching headache for anybody at 175. Sam would be the one giving ground here, and he might not like the experience of a shorter man burrowing under him and counter punching him from long range. Charles could beat him, but he'd likely have to get off the floor to do it. Hagler had the chin, right jab and lateral mobility to pull it off if he entered the ring in the proper frame of mind (assuming the Petronelli brothers manage his corner properly). Langford wanted no part of Jeffries. Choynski drew with Jeff over 20 rounds, and hit him with the hardest punch he claimed he ever took. If anybody could slug it out with Sam and take him out at either 160 or 175, Chrysanthemum Joe (who taught Jack Johnson how to thrash Langford) might be just the man to do it.
I'm not surprised Langford did not want to fight Jeffries.Jeff had his last fight as champion on 26th Sept 1904, he scaled 219lbs.Langford was then 21years old, a month later, 5th Sept ,Langford scaled 142lbs against Joe Walcott , he was fighting lightweights, and the occasional welter during Jeffries reign.
I would not bet the contents of Primo Carnera's spit bucket on any light heavyweight defeating Sam Langford. I wouldn't confidently predict that any heavyweight would beat him either.
That's a very simplistic view of those fighters. Both were excellent technically, they just had the balls to get down and dirty when the time called for it.