Of guys who participated but never won: British Bulldog.
He was participant #2 to Shawn in '95. And was the last guy eliminated after he thought he had already won. So he went the entire distance just like Shawn did.
But he never had a big 'Mania match at WrestleMania 11.
Of guys who "won": Luger.
Even though he only co-won. And really, Bret won and went on to win the title at Mania12. But Luger was a flop.
I disagree with Flair in 1992. He won the WWF title by winning the Rumble. And he had a main event match defending it against Savage. Wouldn't call that a flop.