Ali was without question a top 10 fighter during the time he was forced out of the game due to his refusal to be inducted. He just couldn't get in the ring to prove it.
I could agree with your argument, until the moment Ali showed real quality and offically retired to thus recognize the winner of Frazier and his good friend Jimmy Ellis as new champion.
Hopkins has been top10 since 1992 probably going on 20 years Hopkins probably has one of the longest top5 streak as well, going back to 94
Its a myth that Chuvalo was rated in the top ten continuosly for as long as some people claim. You can check the records of the WBA, WBC, Ring magazine, and Boxing illustrated and during his career he was bumped out of the top ten several times.
Unfortunately, the divisions didnt exist, for most of the time, but the question asked for common sense and judgment. So, i think that the record must go to Bob Fitzsimmons. He has a case of being a top 10 contender from Lightweight to heavyweight from 1881 or 1882 when he won the New Zealand lightweight championship to 1909 when he was knocked out by heavyweight contender Bill Lang. That is 27 years, which is an absolutely enormous performance.