A fighter can be an ATG either through sheer dominance by successfully defending their title (s) for a long period, grabbing titles from different weight classes, or beating other great fighters. Which achievement do you value the most out of the 3 if you were to rank a fighter based on these merits?
The one and only thing that matters is who you beat. If you dominated, who did you dominate? If you jumped up in weight, did you just fight a bunch of nobodies? These are the things you have to keep in mind. At the end of the day it is; Who did you beat, And when did you beat them?
Of these its title defenses depending on the quality of the matchups. Weight jump matters but I prefer using height. People make too much out of 10-20 pounds. Number of HOFers is a bad metric because its not a solid statistic. Its subject to change and for modern fighters its likely to change. If we know whose a HOFer its only going to be the top fighters of an era theres not much data there.