Reach Time =/= Progress?

So I've played Halo Reach since it first came out and played it a lot, yet noticing most people my rank played less and earn more credits and ranks per day than I actually have been able to (stuck at ~10,000 credits as a Lt.Colonel grade 2 at 1-2k per day) with no chance for any big amounts of money or experience coming in. So for anyone who still bothers to play this game, What's the best legit way to rank/get credits besides AFK/Party/Firefight Boosting, Commendations, or Challenges? All of the above are either too time consuming, or too risky to do without getting banned, or have little payout. Also, searching on Google and B.Net only gave results from stuff months ago that has been patched already.