WARNING, BOOK SPOILERS IN THIS POST. IF YOU DO NOT WANT GLASSLANDS SPOILED FOR YOU, SKIP RIGHT OVER IT AND ANY POSTS QUOTING IT.
Right, well here’s the explanation(s) for the Elites:
Q: Why aren’t they well armored or armed?
My A:
If you read Glasslands, you can tell the Elites are in a state of anxiety and disrepair after the war. They were all committed to being soldiers in the Covenant because lesser races could handle the less honorable duties. As such, at the end of the war Sanghelios as a whole is in a state of awkward disrepair. Very few living Elites can farm, repair, and maintain their cities/ships/vehicles very well. Naturally, their armed forces are likely to have become more or less ragtag.
Q: Why would they be working with other Covenant!?!?
My A:
Their only true enemies are the Prophets and Brutes. Grunts were even present on Sanghelios after the war; many seemed to continue to service the Elites (whom one would think are more fair to them than the Brutes would have been). Due to their menial and manual labor skills, they are probably invaluable to the Sangheili. Also, in lieu of having a large standing army with working armor and shields, Grunts serve as good cannon fodder when in need.
Jackals have reverted to their pirating/mercenary ways, and some are known to work with Elites as well. Hunters honorably dedicated many of their services and forces to the Elites as opposed to the Brutes. Some of course worked with the Brutes, but nonetheless many Hunters remained with the Elites. It is feasible to believe that some Hunters remained with the Elites as part of their fallen army.
Since we don’t know what species (I think?) are involved in assaulting Chief, I can’t say why they’re all working together in armed actions unless it is the above species.
Q: Why would they attack Chief? Didn’t we make nice?
My A:
Well, we were allied primarily due to a matter of circumstance. We /needed/ eachother to stop Truth. As evidenced in Glasslands, only select parties were really interested in seeing the Elites and humans become long standing allies. Lord Hood and the Arbiter as well as anyone loyal to them wanted to see the alliance happen, or at least get along decently. Others like O.N.I. and older Sangheili churches want the two races to remain apart- ONI wants the Sangheili to initiate civil war and keep their race on their knees. The Sangheili extremists want to wipe out humanity before they have the chance to rebuild. It’s feasible to believe that the group assaulting you in Halo 4 will be of the faction that does not want an alliance- We will find out more as the sequel to Glasslands is due before Halo 4. At the end of Glasslands, a major explosion had just taken place on Sanghelios, foreshadowing the potential civil war.
Hope this information helped you all!