: I'm not sure I buy that Halo 5 was about trust. It doesn't seem to have
: anything concrete to say about trust, at most "trust these Spartan
: guys because they're saving you and shooting bad guys", or
: "don't trust AIs who say really shady things about controlling places".

As far as what it has to say, I'd say it's about learning to trust or not losing faith, if it wasn't for the notable exceptions I listed. Including those I'd say it's more of a statement of complexity or a question, "You should trust people-- or should you?"

: Is it intentionally a recurring element, or just an element
: that appears a lot but isn't a focus of the story? That's the question.

well, quite
I really don't know, but I think maybe even the fact it can be read that way, that there's enough to partially support a deeper interpretation even if it's not intentional or widely seen, is probably a good thing. There's enough story there to read into it, unlike many games including arguably some other Halo games.