Lewis/Holmes/Tyson/Liston/Marciano

You make valid observations. Faulting Liston for the manner in which he lost to Clay/Ali is fair enough but I personally don't hold it against him too much considering the circumstances. Ali is the greatest ever in my book and Liston was drinking more than training at that point.

My big faulting with Evander is essentially a lack of dominance, combined with the fact that he LOST his trilogy against Riddick Bowe who isn't an all time great. The fact he never really a stretch like Tysons run through the division in 85-89, and Listons during 58-62 hurts him a fair bit in my opinion.
However, on the plus side Holyfield may have faced more good fighters than anyone in the history of the division. Lewis 2x, Bowe 3x, Moorer 2x, Tyson 2x, Ruiz 3x, Foreman, Holmes, Mercer, Stewart, Thomas, a motivated Cooper and Dokes, Byrd, Valuev, Ibragimov, Rahman is an incredible set of names and no one in history goes through that list unscathed and one has to keep this in mind.
But, it's hard for me to rate a guy that lost a trilogy to a non ATG while very close to his peak any higher than about 10th. But I weigh head to head a bit more than most so on other lists I can see him a bit higher due to his overall body of work.