how often does the leaderboard update
it would seem your score is mostly rated on how many games you play and who ever has the most points at the end wins over the 4 week period?
The scoring system was outlined in this Bulletin:
http://blogs.halowaypoint.com/Headlines/post/2013/07/10/The-Halo-Bulletin-71013.aspx
The scoreboard doesn’t update as instantly as the Waypoint Halo 4 stats, but usually within a couple hours.