Peter Maher vs Bob Fitzsimmons - great example of very good fighter against ATG. He troubled Fitz, but Bob won both fights and destroyed him in rematch.
Bronko Mckart was a very good fighter that was trained by the great Bill Miller. He cut his teeth sparring with a lot of great Michigan fighter's and competed all over the midwest beating some quality guys on the way to winning a belt at 154. He just could never get by a great fighter named Winky Wright. He put up a good fight in the first match but you could see the separation of talent in the 2nd and 3rd fight. Bronco fought on for a while with up and down results while Winky went on to beat Mullings, Mosley twice, Tito, Quartey and probably should have got the decision against Taylor. I had him losing a close fight to BHOP but he more than did enough to get into the hall of fame.
Patterson was a good fighter who lost to Liston who was a very good fighter who lost to Clay who was to become a great fighter.
I can remember reading a fair bit about Bronco Back in the day, seemed to get about and fight everyone.
My personal criteria is number #1 A great fighter must defeat a great fighter or fighters when that/those fighter are still relevant. #2 A great fighter must have longevity, and face a number different styles and dominate good/very fighters while their still relevant. #3 A great fighter must show adaptability. #4 A great fighter must have a great/ very good chin, and a great will to win through major adversity .#5 A prime great fighter can have a loss or two providing that the fighter they lose too is also considered great/very good. And if possible they avenge that loss. #6 Great fighters can have any style, as long as they consistently get the job done. Both Curry and Camacho had the ability to be considered ATG's But both fall short with dealing with adversity, Curry with his unreliable chin, both without a PRIME atg win.
Bronco was a tough dude. I remember seeing him as an amateur and he was always tough and well prepared. He just didn't have anything special about him that put him over the top or that made him elite. There was a few guys like him at 154 in that era like Verno Phillips that were solid pro's.
It is the difference between a HOF and an ATG ( Top 100). A guy like Nunn for example is a HOF but an ATG.