Young only became a contender when Frazier's days as a contender were over. Lyle was close to getting a title shot against Frazier but he was derailed by Jerry Quarry.
joe was not afraid of anyone but its clear by the matchmaking that his people were "selective" after the 1st ali fight. its like they knew he was damaged goods. the chalengers he fought after ali were not realy title worthy. Foreman was the first world class rated guy joe defended against since the 71 ali epic and joe made him look so much beter then he was. After that when there were guys like norton, mac foster, lyle, shavers availible they selected bugner. between the last two fights with ali his braintrust selected two guys he had already beat ellis and quarry who like him were leftovers from the late 60s era. frazier was an excelent champion in his day he won his key fights by ko machen,chuvalo, mathis, ellis and quarry and beat an undefeated all time great. the record proves It was down hill after that, he never won a genuine key fight after that. to rate freazier fairly its pre ali and he was far beter than guys like norton, lyle, shavers etc in that period. joe was stricktly a late 60s champion in the way dempsey was strictly an early 20s champion.
What does duck mean ? Did he go out of his way to fight them, no. Was there pressure at any point or him to fight either one, no. Was either a mandatory challenger for his title or mentioned in a title elimination, no. Would either have been a tough match up ? Both likely although I feel he beats both.