Two completely different types of games. Halo is a fps, straight and simple. So you're going to have a rank system for multiplayer. Destiny is an rpg/fps. Leveling up from experience is a key to all rpg's. Grinding & farming are almost a huge part of any rpg. You'd never be able to beat ruby or emerald weapon in ff7 without hours of level grinding and getting better weapons & gear. That's just one example out of many. If you want a great rank system like halo produced. Wait for halo 5 to come out, hopefully it delivers. But destiny's level system is spot on for the game type that it is.