I recall reading a version of the Book of Lists from around 1979-1980 where boxing experts from Ring Magazine were asked to list the greatest heavyweights of all-time.
I don't recall who was #1, but Ali was in the middle of the pack. Reading it in the mid-90's, I was somewhat surprised because Ali's reputation had taken on legendary proportions.

Of course, an athlete's place in history isn't established until we can view it from some historical perspective, but I believe that while Ali was a great champion, his abilities today are somewhat overstated as his career benefited from several questionable decisions. Many agree that Ken Norton was robbed in Yankee Stadium, Frazier won the second fight, and I believe that Jimmy Young-a little known challenger in the mid-70s beat Ali. Many defended the questionable decisions in these fights at the time by saying, To beat a champion, you have to knock him out."

When Spinks defeated Ali in 1977(?), the fight was not that close, and Ali, tired and hurt, tried valiantly for a knockout in a stirring final round. He had Spinks in trouble until Leon delivered a stiffening right. Even that fight was a split decision.

Speaking of Spinks, by the way, wasn't the U.S. Boxing team of the 1976 Olympics their greatest? Howard Davis, Ray Leonard, Michael and Leon Spinks. Can't recall the others right now.