Iyo ,are there any contender s , guys that faced linear Champ s and lost , that could maybe have beaten Frazier as champ ?
"Could" have is a big qualifier and I think there would be more than you think. Now if you mean "a guy that never won any belt at all" then it gets consideraably narrower. I think any skilled, accurate and big-punching heavyweight "could" have a chance of beating Frazier.
Remember Smoking Joe Frazier, as I said was a terrifying locomotive. But after The Fight Of The Century on March 8 1971 against a come backing Muhammad Ali, he left the greatest win of his career in the ring that night, he would never be the same again. He had title defenses against Terry Daniels in January 1972, and against Ron Stander in May 1972. When he went into the ring against George Foreman on January 22 1973, in Kingston, Jamaica, he was sadly spent. That was the heavyweight that did beat him. As another poster pointed out, Mac Foster was a possibility. I believe that friendship aside, Ken Norton could have, he broke Ali's jaw on March 31 1973 in San Diego, California. Norton would continue to be a thorn in Ali's side for the rest of the decade.