In the Locke trailer he calls Chief a traitor…but to whom? And the way Chief talks in his own trailer is less like talking to Locke and more like talking to ONI.
“Is this what you wanted?”- possibly referring to the Covenant returning to full power after the ONI’s assistance to the Servants of Abiding Truth and perhaps the assassination of The Arbiter.
“…Everything you’ve compromised, everything you’ve done…”- Possibly to the ONI compromising the truce they had between Humans and Sangheili because of their paranoia, and putting many people at risk.
“My mission is just beginning”- Chief is going to try to dismantle ONI.
Chief knows very well how many in ONI are clever, competent and pro-human. How many researchers, civilians, professors, scientists, analysts and journalists there are. how many good agents, operatives and officers. And also that not all high ranked members are -Yoink-.
I don’t see chief going against ONI in the sense he wants to dismantle it, but it isn’t impossible (but still it’s improbable) that he goes against CINCONI for example, or another secondary group/team/section.
It wouldn’t surprise me, though I reckon it’ll probably be more that he’s going up against corrupt leaders of ONI rather than the organisation itself. Afterall ONI was useful during the war and they did help win the war. However once they started supporting the Servants of Abiding Truth it could be because their leadership has been compromised
and gone evil