I'm probably LTTP on this. But something I just noticed about the Commendations: they have a cap. The Legendary Guide:
You can earn Credits for completing a total of 60,000 headshots, but only 20,000 in each of the three modes. A player who manages to accumulate 20,000 headshots in Firefight, for example, can no longer receive Credits for headshots in that mode, but may still earn headshot Credits in Campaign and Multiplayer.
So right now I have 11,176 / 20,000 total for Dome Inspector in Firefight. Before the end of the year, I won't be earning credits for headshots any longer. Since that's the mode I primarily play, my rate of credit accumulation will drop sharply. Kinda bummed about this; one of the reasons I like the Commendation system is it rewards across all game modes. But a few months after release I won't be able to earn any cR for the primary kill method of the game mode I play most.