Exactly. Let me restate my original question:

Munky opined that there were probably a lot of developers at 343i who were fans of the original Halo games, and it would suck to finally get to work on Halo only to see it ruined. I countered by saying that the people who develop the individual parts of the game get to see their vision of Halo realized, so it's a win-some lose-some scenario. Besides, no two Halo fans can agree on where the next game should go and what changes it should make.

And if a low-level game designer is dissatisfied with the direction of Halo 5, how does he make that dissatisfaction known? If it's within the realm of his expertise, he talks to his supervisor. If not, what can he do then?

Lets say that one of the UI artists dislikes Halo 5's story and thinks that the Promethean weapons should be more esoteric than the generic FPS weapon set of pistol/shotgun/bullet hose/precision gun/sniper rifle/rocket launcher. When does he take his concerns to the people in charge of these aspects of Halo 5? When does he get a slot in Brian Reed's packed schedule to talk about his concerns?

Why would they listen to him? He wasn't hired to be a writer or a gameplay designer, so what does he have to offer? If he does have relevant qualifications, he still hasn't been playing all the gameplay prototypes or attending the writing meetings. He doesn't know what's been tried, so his suggestions may be superfluous.