You know, with the advertising harping on whether Chief is friend or foe, that theme of misplaced trust is a good one; it applies to relationships including pretty much every character in some manner, so maybe in a way the advertising really wasn't (that far) off the mark, it just focused on the Chief's part of the narrative. But if we get that understanding of trust/mistrust just from his part, we can start to see that trust/mistrust in all those other arcs you mentioned. Halo 5 was really about who to trust, who is trustworthy, preception... beyond just Chief and Locke. hm.