Excuses. Ali can play the "if" game too. If Ali wasn't exiled for boxing for 3.5 years Frazier doesn't touch him and probably gets stopped. If Ali had more tune-up fights and therefore better conditioning and less ring rust he wins the first fight.
There is a consensus now that Ali took the Frazier fight too early, but he didn't have a choice because the Supreme Court could have delivered their decision on his court case at any point, so he risked going to jail for draft dodging before cashing out on the Frazier fight. So, "if" he only had more tune-up fights.
This is an urban legend. Mark Kram (having an anti-Ali agenda) twisted a throwaway comment Ali made and printed that as a fact.
Ali said a lot of shit just to be dramatic (e.g. threw his Gold medal in the Ohio river). In an effort to give Joe props and stress how hard the fight was he said he almost quit. Everyone knew to take Ali's comments with a grain of salt. He was an exaggerator to put it mildly. If Joe came out for the 15th, Ali would have been right there with him. Anybody who thinks otherwise is naïve. Frazier was absolutely pummeled in the 13th round and was on his last legs in the 14th, Ali obviously knew that. Joe Frazier might have died in the ring if they let him come out for the 15th.
I'm a fan of Ali but don't entirely agree with this. I haven't heard of a fighter having two tune-up fights against world-class competition and not be ready. I'm not saying Ali was at his best but he hadn't fought somebody like Frazier. Ali could have been at his best but he'd have always struggled with Frazier,their three fights against each other proved that. As for the third fight anything could have happened if they continued. But it was a good thing that they stopped the fight.