Martial arts, like any hobby, seeks to be accessible to anyone. This means that students come in with a wide range of initial capabilities and overall potential. Some students intuitively pick up the basics, and then stall out. Some start slow and steadily progress. Some will never be coordinated. Some start fast and turn into metaphorical gods of the sport. Hopefully they won't all progress through the belts at the same pace. The students that learn faster should rank up faster, but to a point, everyone should rank up. They should be judged in accordance with their abilities, and rewarded for the gains they have made in their understanding and ability. With that said, at some point the rank gets high enough that you become qualified to be an instructor, or even higher to where you could be a master (or equivalent in your art). If a C student becomes a teacher, then their A students will be the equivalent of someone else's C students. Maybe they have a student or two that can elevate themselves above. Maybe not. Is there a point at which rank progression should switch from progress to merit? What point would that be in your art? Or should it always be progress, or always be merit?