You apparently missed the whole point of this thread. The question was: Having legit credentials (which includes being on par with another titleholder) automatically disqualifies him from this thread.
Ray Austin was not very good but Gerrie Cooney was worse . On which victory of his can you base your claim that he was any better ? the punching out of a downed old chinny Norton ? the cutting of a post prime Jimmy Young ? or the dead old Lyle fight ? can someone tell me if at least the lyle fight was a technically legit stoppage ? Fact is that Austin's resume is much more impressing (not that it's impressing) .
Wepner was a solid top #15 contender when he met Ali in 1975. I think the magazines and WBA/WBC may even have rated him within their top 10 for bit. By no means was Wepner the worse heavyweight challenger of all time.
Jean-Pierre Coopman was catapulted way, way over his head when he met Ali in 1976. By any measure, Coopman was barely a top 30 heavyweight in terms of ability, if that. He hadn't beaten anyone, and I think he had lost to lightheavyweights. Not in any way was Coopman a bonafide top 10, 15 or even top 20 heavyweight when he fought for the title. He may have been the worst challenger of all time at heavyweight.
Roman is definitely a candidate. Someone mentioned Dave Zyglewicz, who was just a local NY state clubfighter. Zyglewicz is a candidate too. Pete Rademacher was certainly the least deserving challenger of all time. Maybe not the worst, but definitely the least deserving.
I havent picked my three yet but, I nominate John Finnegan as the worst and least deserving of a title shot. Finnegan fought Jeffries in 1900, here is his record,going into the title challenge. 4-2-4 The win loss records of his opponents, is distinctly underwhelming. Finnegan met one class man prior to fighting Jeffries ,Gus Ruhlin, here's what happened. weighed but 180, and he looked like a boy beside the champion." (Brooklyn Daily Eagle) 1900-01-31192Gus Ruhlin195 This content is protected - This content is protected - This content is protected Genesee A.C., Utica, New York, United StatesLKO420 Finnegan of Pittsburgh was on his back ten seconds after the first bell. He beat the count and survived the round, but took a beating in the second round, only saved by the bell. In the third round, two hard lefts knocked him through the ropes. He crawled back in to beat the count again, but his seconds had to carry him to his corner. Seconds into the 4th round Ruhlin dropped him again, and inside the next minute and a half he dumped "The Pittsburg Stogie" on the canvas four more times. As the police moved to stop the fight, Richard McCormick, Finnegan's manager, ran into the ring and carried his man to his corner. And here is an account of his "title challenge" 1900-04-06180James J Jeffries240 This content is protected - This content is protected - This content is protected Cadillac A.C., Detroit, Michigan, United StatesLKO110 time: 0:55 | referee: George Siler World Heavyweight Title "Finnegan landed the first blow as they came to the center of the ring, and Jeffries then put his left on the Pittsburgh man's jaw and he went to the floor. Finnegan came up in a few seconds only to be sent to the floor again with a blow in the same place. He stayed down longer this time and when he again rose he was in visible distress. He had hardly assumed a fighting position before the champion put his left in the pit of his stomach and Finnegan went down completely out. Referee Siler counted the seconds off and when he stepped back it was seen that Finnegan was crying. He staggered to his feet, reeled against the ropes and his seconds rushed into the ring and carried him to his corner. It was several minutes before he recovered sufficiently to leave the ring. Jeffries said he weighed 220, but he looked 30 pounds heavier. Finnegan weighed but 180, and he looked like a boy beside the champion." (Brooklyn Daily Eagle)
The Smith win was many years prior, though. But Pachilles' pick seems to have been even much worse than Carpentier. Then we have the outstanding question if Miske was seriously ill or not when Dempsey defended against him.