I certainly don't blame Wills for turning it down. As janitor said, it looks like Rickard's plan was to let another contender take care of Harry. Going by what happened against Sharkey in 1926, it looks like he'd have gotten his wish if Tunney had faced that version of Wills. Rickard was probably just as satisfied Sharkey did the deed. Wills did get royally screwed, and it sucks that the politics led to fights with some of the top white fighters not happening, either.
It was categorically stated during his trial that Tunney never had any intention of fighting Wills and that such talk was just to place him in direct line and on the same level as Dempsey's top challenger. It was a promotional stunt. Thats a fact and it was born out by the testimony of Tunney, Tim Mara, and the cables back and forth between Tunney and his people at the time. There was never any real call for Greb to fight Wills. I think at one point, if memory serves, Greb said something to the effect that he would fight Wills to get to Dempsey if he had to but it was kind of an off hand remark and never really went anywhere. Greb, by the way, had a great deal of respect for Wills and not only thought he would beat Dempsey (which counts for something because Greb was absolutely fantastic at picking fights) but also stated that Dempsey was ducking him.