Fitz' weight jumping feats are impressive, but his dominance at middleweight are every bit as impressive as well. No one was any more dominant at one particular weight than Fitz was at middleweight. In fairness, Ali is dreadfully underated on a pound for pound basis by most, so i would not argue with Ali being placed in the top 10, it is just that he simply wasnt as dominant for so long on a pound for pound basis as Fitz was. Fitz knocked out every good middleweight he fought, usually in a handful of rounds. That is unbelievable. Plus, as a middleweight, he also knocked out the very best Heavyweights in the world and knocked most of them out, usually in a handful of rounds. I dont think that anyone really appreciates just how dominant he was.
There is no comparison between Lopez's level of opposition and Pep's. You guys seem to be underrating the man's body of work. Weight-jumping doesn't mean a damn thing, if you ask me. Sure, it helps out certain fighter's pedigrees, but it's not like it's a prerequisite for a high ranking. Dominance, performance, ability, longevity, etc. can play just as high a role, and few were ever more impressive than Pep in those regards. Certain fighters just aren't physically cut out to play the weight-jumping game, whereas others (who may not even be as talented at their prime weights) are. It doesn't necessarily mean the latter group are the better fighters. I think this frame of mind is what has lead to the overrating of Pacquiao lately. Great fighter, no doubt, but not as much as many would have you believe.