Since Darcy died at 21 and had his last fight at 19 I don't see how anyone could say with any certainty that even Harry Greb would have beaten him. They had a few common opponents some of which Darcy beat far more easily (McGoorty,Chip) and some of them Greb did better against (Jeff Smith). Of course Greb would go on and paste some amazing fighters but what's to say Les wouldn't have done something similar (of course it's just as likely he wouldn't have either). Darcy was by all accounts a phenom as was Harry but unfortunately Les never got to even half complete his career whereas Greb did, with truly legendary results. But as for the thread I doubt Greb ducked anyone. He was fearless and the only fight that could've feasibly occured of his that didn't would of been a fight with Langford. Phew imagine that one but even then they were at different stages of their careers so it was probably never realistic anyway.
And we can't forget that Fitz and Langford blatantly, and without apology, ducked the father of Lizzard and Gizzard (and grandfather of Ezzard), Buzzard Charles.