If I recall correctly, I believe 343i houses roughly 300+ employees. I have the imagine the team is well staffed and has the manpower, however I'd say 85% of the team is working toward Halo 5 Xbox One, which 10% on Halo 4 and the other 5% on Spartan Assault/Web team/etc.
It almost seems that when they launched Halo 4, they had a wonderful sustain team for the next 2-3 months. Then when development on the next Halo title ramped up, they just put Halo 4 in the rearview mirror. The sustain team is wonderful for being active week after week... But something doesn't click. The changes they're making just isn't...working. They don't get it or want to get it. They're not responding adequately enough to the community. Well, by community I guess I mean HaloGAF.